Remove dependency on test_support_base from cast

I greped the entire media/cast directory now there's only one target
depending on test_support_base which is cast_unittests.

TBR=scherkus
BUG=323769

Review URL: https://codereview.chromium.org/90303002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237525 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237525