kcms/keyboard: handle botched 5.21.0 migration

Since we shipped a botched migration script for 5.21.0, we need to
ship a new migration script that un-botches the effects of the 5.21.0
script. We also change the ID of the plain kcminput_repeat migration so
that we can distinguish between the botched migration and the non-botched
migration, and only reverse migrations applied by the botched migration.

BUG: 431923
FIXED-IN: 5.21.2