Do disable extensions for Android, too

I started running into mysterious trouble when some code still thought it
should be looking for extensions, although (perhaps) other code was not
willing to support such, or something. Some confusion caused by my recent
changes to make the conditional support of features more fine-grained.

Change-Id: I61758cb06054ceb038d200bc95615b5b85ed0f7b

configure.ac

@@ -2150,9 +2150,8 @@ fi
 AC_SUBST(DISABLE_DBCONNECTIVITY)
 
 if test -z "$enable_extensions"; then
-    # For iOS disable extensions unless specifically overridden with
-    # --enable-extensions.
-    if test $_os != iOS; then
+    # For iOS and Android disable extensions unless specifically overridden with --enable-extensions.
+    if test $_os != iOS -a $_os != Android; then
         enable_extensions=yes
     fi
 fi