Also prune src/webkit/tools/layout_tests/test_expectations.txt since they've
all been upstreamed or resolved.

Review URL: http://codereview.chromium.org/2997004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@52308 0039d316-1c4b-4281-b951-d872f2087c98