android: Fold all_android.gyp into all.gyp.

All other platforms have their targets in all.gyp. Android didn't during
bring-up, but enough stuff works by now that there's no need for the
separate all_android.gyp file any more.

BUG=330631
R=yfriedman@chromium.org
TBR=rsleevi@chromium.org

Review URL: https://codereview.chromium.org/139743016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246782 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246782