yarn scripts: Remove several aliases for simple commands.

As Greg suggests at
  zulip#4700 (comment).

These made sense before `tools/test` existed, and they were good
shortcuts for complicated commands. Now, even if they still work,
they're just obstacles in the way of getting familiar with
`tools/test` and all its features.

package.json

@@ -17,13 +17,6 @@
     "build:android-nokeys": "cd android && ./gradlew :app:assembleRelease",
     "build:ios": "cd ios && xcodebuild -scheme ZulipMobile archivexcodebuild -scheme ZulipMobile archive",
     "test": "tools/test",
-    "test:full": "tools/test --full --coverage",
-    "test:lint": "tools/test lint",
-    "test:lint-full": "tools/test lint --full",
-    "test:flow": "tools/test flow",
-    "test:prettier": "tools/test prettier",
-    "test:prettier-full": "tools/test prettier --full",
-    "test:unit": "tools/test jest",
     "prettier": "tools/fmt",
     "prettier-full": "tools/fmt --all",
     "test:flow-coverage": "flow-coverage-report -i 'src/**/*.js' -x '**/__tests__/**' -t html",