Fix non-goma android build after r238630

dirname outputs "." when given an empty argument, which gyp rules then
interpret as goma being available.

Remove ANDROID_GOMA_WRAPPER which is no longer used, and use GOMA_DIR
directly for android build.

BUG=
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=238718

Review URL: https://codereview.chromium.org/104563004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238727 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238727