Remove unused test data under content/common/gpu/testdata/.

BUG=332315
TEST=none

Review URL: https://codereview.chromium.org/183923037

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255639 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255639