BeforeSpecialMobileDiffDisplay hook: Only accept RevisionRecord
BeforeSpecialMobileDiffDisplay hook: Only accept RevisionRecord

Compatibility was added so that MobileFrontend could switch from
Revision to RevisionRecord, but now that the switch has occurred no
need to keep checking to see if a Revision is being passed

See [1] for the MobileFrontend change that required compatibility

[1] https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/MobileFrontend/+/e42c52527b7c8083e6395bee7a7981394fb0db4e

Bug: T246284
Change-Id: Ie320454a0e90d7f98004a3b776010aff784bbf4d

wikimedia/mediawiki-extensions-Thanks,wikimedia/mediawiki-extensions-Thanks,wikimedia/mediawiki-extensions-Thanks