Following the config change to drop MFSpecialCaseMainPage we can drop the code that special cases main pages in MobileFrontend. This will make our codebase lighter and easier to maintain, will make our product easier for editors to understand and allow us to resolve the longstanding epic T32405. While we don't drop it there is a risk that it could be enabled by production wikis.
- The config flag MFSpecialCaseMainPage is dropped
- The class LegacyMainPageTransform is removed from MobileFrontend
- Resolve the epic T32405