Clean up unused constant globals

Found by clang's new -Wunused-const-variable.

BUG=290204
TBR=mark, acolwell, agl, alexeypa, markus, brettw

Review URL: https://codereview.chromium.org/25849004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226888 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226888