AW docs: link to WebView-specific docs

This removes the section on webview_instrumentation_test_apk from
Android's general test docs, and links to WebView team's docs instead.

This also fixes a typo: "Android WebView" should be two words.

R=agrieve@chromium.org

Bug: 918221
Test: Upload to gerrit > open file > click "gitiles".
Change-Id: I083b42fbf0f35ec401bc510527743dbcd4cedfef
Reviewed-on: https://chromium-review.googlesource.com/c/1464357
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631197}

docs/android_test_instructions.md

@@ -243,13 +243,9 @@ ninja -C out/Release chrome_public_test_apk
 out/Release/bin/run_chrome_public_test_apk [-vv]
 ```
 
-AndroidWebView tests:
+Android WebView tests:
 
-```shell
-ninja -C out/Release webview_instrumentation_apk
-ninja -C out/Release webview_instrumentation_test_apk
-out/Release/bin/run_webview_instrumentation_test_apk [-vv]
-```
+See [WebView's instructions](/android_webview/docs/test-instructions.md).
 
 In order to run a subset of tests, use -f to filter based on test class/method
 or -A/-E to filter using annotations.