android: Stop calling md5sum for ant_obfuscate step.

All inputs except instr_stamp are passed in the command and instr_stamp
is a single fixed file, so this isn't necessary. No functionality change.

BUG=177552
R=cjhopman@chromium.org

Review URL: https://codereview.chromium.org/180033009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255451 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255451