Remove PlatformAppBrowserTest.ShellWindowRestorePosition because it is
flaky and superseeded by AppWindowAPI.TestRestoreGeometryCacheChange.

BUG=304555, 238310

Review URL: https://codereview.chromium.org/96813003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238078 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238078