[Android] Simplify check for --app-{local-path,root,url} in make_apk.

The existing check for those parameters is very convoluted and hard to
follow.

Instead, only error out in one of the following conditions:
* None of --app-local-path, --app-root and --app-url are passed.
* Either --app-local or --app-root are passed but not both.

We consciously consider it fine for all parameters to be set, in which
case we use --app-url's value.