[ci] Optimize Android shell apps (expo#7888)

# Why

- Let's keep secrets secret!
- Makes Turtle deploy faster and use less memory and storage

# How

- Removed the `decrypt_secrets…` from `shell_app_android` job,
- Removed the `yarn install` from `tools-public` (Turtle doesn't use anything JS-y from within `tools-public`, the only thing it uses is the `check-…macros.sh` script).
- Removed the `android/versioned-abis` directory as it used a couple of MBs and we are sure we would never use it in standalone apps.
- Annotated the whole `buildAndroidTarballLocally.sh` script for future reference.

# Test Plan

The shell app build process has been tested on an `sdk-37`-based branch in expo#7889 ([job](https://app.circleci.com/jobs/github/expo/expo/143387)).

Pushed the shell app built as a part of expo/turtle#209 to staging and it built as expected.

.circleci/config.yml

@@ -706,12 +706,7 @@ jobs:
     steps:
       - setup
       - run: echo 'export S3_URI=s3://exp-artifacts/android-shell-builder-$CIRCLE_SHA1.tar.gz' >> $BASH_ENV
-      - decrypt_secrets_if_possible
       - install_yarn
-      - yarn_install:
-          working_directory: ~/project/tools-public
-      - yarn_install:
-          working_directory: ~/project/tools
       - yarn_restore_and_install:
           working_directory: ~/project/tools/expotools
       - run:

buildAndroidTarballLocally.sh

@@ -9,19 +9,28 @@ TEMP_DIR="/tmp/android-shell-app"
 mkdir -p $ARTIFACTS_DIR
 rm -rf $TEMP_DIR
 mkdir -p $TEMP_DIR
-ln -s ${ROOT_DIR}/tools-public $TEMP_DIR/tools-public
-ln -s ${ROOT_DIR}/secrets $TEMP_DIR/secrets
-ln -s ${ROOT_DIR}/template-files $TEMP_DIR/template-files
+
+# only check-dynamic-macros-android.sh is used
+mkdir -p $TEMP_DIR/tools-public
+ln -s ${ROOT_DIR}/tools-public/check-dynamic-macros-android.sh $TEMP_DIR/tools-public/check-dynamic-macros-android.sh
+
+# we use the root android project as a shell app template
 ln -s ${ROOT_DIR}/android $TEMP_DIR/android
+# We wouldn't want to use any versioned ABI in a standalone app
+# and it makes the shell app smaller.
+rm -rf $TEMP_DIR/android/versioned-abis
+
+# root package.json defines a dependency on react-native-unimodules,
+# which we require when building the shell app
 ln -s ${ROOT_DIR}/package.json $TEMP_DIR/package.json
-ln -s ${ROOT_DIR}/expokit-npm-package $TEMP_DIR/expokit-npm-package
+
+# packages are used by the optional-modules-linking-code in XDL
+# see xdl/AndroidShellApp.js
 ln -s ${ROOT_DIR}/packages $TEMP_DIR/packages
 
-# generate dynamic macros
-mkdir -p $TEMP_DIR/android/expoview/src/main/java/host/exp/exponent/generated/
-cd $TEMP_DIR/tools-public
+# generate dynamic macros (we can do it here, as the contents are already `ln -s`-ed)
 et android-generate-dynamic-macros --configuration release
-rm -rf $TEMP_DIR/secrets
 
+# build the artifact
 cd $TEMP_DIR; tar -czhf $ARTIFACTS_DIR/android-shell-builder.tar.gz .
 rm -rf $TEMP_DIR

template-files/keys.json

@@ -13,7 +13,7 @@
   "AMPLITUDE_DEV_KEY": "773a3e0a8a28b8b1c3497792df4a5271",
   "REACT_NATIVE_PATH": "../react-native-lab/react-native",
   "UNIVERSAL_MODULES_PATH": "../packages",
-  "CERTIFICATE_HASH": "892B2B46907B26D3E729829AFCE15446B9947450",
+  "CERTIFICATE_HASH": "",
   "FIREBASE_CLIENT_ID": "",
   "FIREBASE_REVERSED_CLIENT_ID": "",
   "FIREBASE_API_KEY": "",