Revert "Add new recentchanges field rc_source to replace rc_type"

No feature flag, and also not deployed on WMF wikis. Asking for schema changes by the time we branch tomorrow is just unfair

This reverts commit e478c230f6d3f1b7638d4443682eff0df7650def.

Change-Id: I125c30e76fa04679cc04ae7b8728ae3a61f35194
Merge "Revert "Add new recentchanges field rc_source to replace rc_type""