test(docs-infra): compile only app for examples with no e2e

With TS 3.7, these examples were running into the error below (e.g. on https://circleci.com/gh/angular/angular/574906#tests/containers/0):

```
============== AIO example output for: /home/circleci/ng/aio/content/examples/observables/
running: yarn tsc --project ./
$ /home/circleci/ng/aio/content/examples/observables/node_modules/.bin/tsc --project ./
../../../tools/examples/shared/node_modules/protractor/built/index.d.ts(5,10): error TS2440: Import declaration conflicts with local declaration of 'PluginConfig'.
../../../tools/examples/shared/node_modules/protractor/built/index.d.ts(5,24): error TS2440: Import declaration conflicts with local declaration of 'ProtractorPlugin'.
error Command failed with exit code 2.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
completed: yarn tsc --project ./
```

This happened because of angular/protractor#5348.

It's unclear why this typings problem does not affect `ng e2e` runs, and only affects `tsc` runs.

For now it seems sensible to alter the tests to compile only the app and not the e2e, since the intent of angular@2cc954d was never to verify the correctness of the e2e in the first place.

We still need a release of protractor that supports TS 3.7 though, but at least it doesn't seem to block our update proper.

aio/content/examples/observables-in-angular/example-config.json

@@ -2,7 +2,7 @@
   "e2e": [
     {
       "cmd": "yarn",
-      "args": [ "tsc", "--project", "./" ]
+      "args": [ "tsc", "--project", "./tsconfig.app.json" ]
     }
   ]
 }

aio/content/examples/observables/example-config.json

@@ -2,7 +2,7 @@
   "e2e": [
     {
       "cmd": "yarn",
-      "args": [ "tsc", "--project", "./" ]
+      "args": [ "tsc", "--project", "./tsconfig.app.json" ]
     }
   ]
 }

aio/content/examples/practical-observable-usage/example-config.json

@@ -2,7 +2,7 @@
   "e2e": [
     {
       "cmd": "yarn",
-      "args": [ "tsc", "--project", "./" ]
+      "args": [ "tsc", "--project", "./tsconfig.app.json" ]
     }
   ]
 }

aio/content/examples/rx-library/example-config.json

@@ -2,7 +2,7 @@
   "e2e": [
     {
       "cmd": "yarn",
-      "args": [ "tsc", "--project", "./" ]
+      "args": [ "tsc", "--project", "./tsconfig.app.json" ]
     }
   ]
 }