Further constrain W0 X-CS setting to mobile Wikipedia, for now.

* In a future state this will be updated to support more projects.
* But for now, the X-CS fallthrough should only be set if it's a mobile Wikipedia.

Change-Id: I2d912409e48d367431d5afb63f8994c2aeb2c9db
Merge "Further constrain W0 X-CS setting to mobile Wikipedia, for now." into production