build: remove kokoro.keystore_resource configuration (#180)

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:
```
synthtool > Executing /tmpfs/src/git/autosynth/working_repo/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:7231f27272231a884e09edb5953148c85ecd8467780d33c4a35c3e507885715b
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/cloud/bigquery/datatransfer/artman_bigquerydatatransfer.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/js/bigquerydatatransfer-v1.
.eslintignore
.eslintrc.yml
.github/ISSUE_TEMPLATE/bug_report.md
.github/ISSUE_TEMPLATE/feature_request.md
.github/ISSUE_TEMPLATE/support_request.md
.jsdoc.js
.kokoro/common.cfg
.kokoro/continuous/node10/common.cfg
.kokoro/continuous/node10/docs.cfg
.kokoro/continuous/node10/lint.cfg
.kokoro/continuous/node10/samples-test.cfg
.kokoro/continuous/node10/system-test-grpcjs.cfg
.kokoro/continuous/node10/system-test.cfg
.kokoro/continuous/node10/test.cfg
.kokoro/continuous/node11/common.cfg
.kokoro/continuous/node11/test.cfg
.kokoro/continuous/node6/common.cfg
.kokoro/continuous/node6/test.cfg
.kokoro/continuous/node8/common.cfg
.kokoro/continuous/node8/test.cfg
.kokoro/docs.sh
.kokoro/lint.sh
.kokoro/presubmit/node10/common.cfg
.kokoro/presubmit/node10/docs.cfg
.kokoro/presubmit/node10/lint.cfg
.kokoro/presubmit/node10/samples-test.cfg
.kokoro/presubmit/node10/system-test-grpcjs.cfg
.kokoro/presubmit/node10/system-test.cfg
.kokoro/presubmit/node10/test.cfg
.kokoro/presubmit/node11/common.cfg
.kokoro/presubmit/node11/test.cfg
.kokoro/presubmit/node6/common.cfg
.kokoro/presubmit/node6/test.cfg
.kokoro/presubmit/node8/common.cfg
.kokoro/presubmit/node8/test.cfg
.kokoro/presubmit/windows/common.cfg
.kokoro/presubmit/windows/test.cfg
.kokoro/publish.sh
.kokoro/release/publish.cfg
.kokoro/samples-test.sh
.kokoro/system-test.sh
.kokoro/test.bat
.kokoro/test.sh
.kokoro/trampoline.sh
.nycrc
.prettierignore
.prettierrc
CODE_OF_CONDUCT.md
CONTRIBUTING.md
LICENSE
codecov.yaml
renovate.json
synthtool > Replaced 'https:\\/\\/cloud\\.google\\.com[\\s\\*]*http:\\/\\/(.*)[\\s\\*]*\\)' in src/v1/doc/google/protobuf/doc_timestamp.js.
synthtool > Replaced 'toISOString\\]' in src/v1/doc/google/protobuf/doc_timestamp.js.

> grpc@1.19.0 install /tmpfs/src/git/autosynth/working_repo/node_modules/grpc
> node-pre-gyp install --fallback-to-build --library=static_library

node-pre-gyp WARN Using needle for node-pre-gyp https download 
[grpc] Success: "/tmpfs/src/git/autosynth/working_repo/node_modules/grpc/src/node/extension_binary/node-v57-linux-x64-glibc/grpc_node.node" is installed via remote

> protobufjs@6.8.8 postinstall /tmpfs/src/git/autosynth/working_repo/node_modules/protobufjs
> node scripts/postinstall

npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents@1.2.7 (node_modules/fsevents):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for fsevents@1.2.7: wanted {"os":"darwin","arch":"any"} (current: {"os":"linux","arch":"x64"})

added 1105 packages from 1301 contributors and audited 6723 packages in 26.535s
found 1 low severity vulnerability
  run `npm audit fix` to fix them, or `npm audit` for details

> @google-cloud/bigquery-data-transfer@0.5.1 fix /tmpfs/src/git/autosynth/working_repo
> eslint --fix '**/*.js'


/tmpfs/src/git/autosynth/working_repo/samples/quickstart.js
  19:40  error  "@google-cloud/bigquery-data-transfer" is not found  node/no-missing-require

/tmpfs/src/git/autosynth/working_repo/samples/system-test/quickstart.test.js
  17:26  error  "chai" is not found  node/no-missing-require

✖ 2 problems (2 errors, 0 warnings)

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @google-cloud/bigquery-data-transfer@0.5.1 fix: `eslint --fix '**/*.js'`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the @google-cloud/bigquery-data-transfer@0.5.1 fix script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/kbuilder/.npm/_logs/2019-03-15T11_09_18_816Z-debug.log
synthtool > Cleaned up 2 temporary directories.
synthtool > Wrote metadata to synth.metadata.

```

packages/google-cloud-bigquery-datatransfer/synth.metadata

@@ -1,19 +1,19 @@
 {
-  "updateTime": "2019-03-12T11:08:39.884575Z",
+  "updateTime": "2019-03-15T11:09:18.828281Z",
   "sources": [
     {
       "generator": {
         "name": "artman",
-        "version": "0.16.16",
-        "dockerImage": "googleapis/artman@sha256:30babbfce7f05a62b1892c63c575aa2c8c502eb4bcc8f3bb90ec83e955d5d319"
+        "version": "0.16.17",
+        "dockerImage": "googleapis/artman@sha256:7231f27272231a884e09edb5953148c85ecd8467780d33c4a35c3e507885715b"
       }
     },
     {
       "git": {
         "name": "googleapis",
         "remote": "https://github.com/googleapis/googleapis.git",
-        "sha": "abd1c9a99c5cd7179d8e5e0c8d4c8e761054cc78",
-        "internalRef": "237945492"
+        "sha": "d358313693b36723eea44832d8bf5a3d64b623ea",
+        "internalRef": "238565258"
       }
     },
     {