Remove Identity API scope approval app from webviewExperimental whitelist

The scope approval app uses the webview.request API, which was
experimental, but isn't any longer.

This reverts r214992 (https://chromiumcodereview.appspot.com/20843004)

TEST=manual test with CHROME_VERSION_EXTRA=stable
BUG=305766

Review URL: https://codereview.chromium.org/26753002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228069 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228069