Migrate recentchanges table to abstract schema
This table is massive but thankfully we fixed most of its complexities
in previous patches.
- Change type of rc_title and rc_source from "varchar binary" to "varbinary"
- Drop default of rc_timestamp
- Change rc_timestamp from varbinary(14) to binary(14) to standardize timestamp datatypes
One index doesn't follow the uniform prefix rule but since it's in a
maintenance script, will fix that in a follow up.