android envsetup: Remove a block that has no effect.

By the time this runs, DEFINES has already been copied into GYP_DEFINES
(see also r246062) and no longer has any effect.

(Also, I didn't find references to CHROME_ANDROID_VALGRIND_BUILD on
cs.chromium.org and the two internal places I looked.)

BUG=330631
R=torne@chromium.org

Review URL: https://codereview.chromium.org/144003010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246096 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246096