Instruct JavaScript modules in MobileFrontend to not show images.

* Currently, thumbnails being showed in dynamic search on zerodot.
* But such search thumbnails should only be showed on mdot.
* We use MakeGlobalVariablesScript due to varying on X-Subdomain.
* This doesn't override $wg globals, so no origin-emitted HTML regressions.

Change-Id: I45a0d00ff957bab6f08f3c78ee235b23675aade7
Merge "Instruct JavaScript modules in MobileFrontend to not show images."