Hygiene: MobileWebCta

This code isn't loaded anywhere and hasn't been logging events
since 31st July 2014 according to the table.

Remove https://meta.wikimedia.org/wiki/Schema:MobileWebCta

Change-Id: Ib5094a49e8492844742c4017183aa31542879c6d
Merge "Hygiene: MobileWebCta"