Disable WebrtcApprtcBrowserTest.MANUAL_WorksOnApprtc for Windows<=XP

Temporary disable due to flakiness
http://chromegw/i/internal.chromium.webrtc/builders/WinXP%20Hideout%20Tester/builds/2653/steps/webrtc_manual_browser_tests_test/logs/stdio

BUG=webrtc:2703

Review URL: https://codereview.chromium.org/111583002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240116 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240116