Update outdated references to the SLRU ControlLock
SLRU bank locks are referred as "bank locks" or "SLRU bank locks" in the
code comments. The comments updated in this commit use the latter term.
Oversight in
53c2a97a9266, that has replaced the single ControlLock by
the bank control locks.
Author: Julien Rouhaud <julien.rouhaud@free.fr>
Discussion: https://postgr.es/m/aLUT2UO8RjJOzZNq@jrouhaud
Backpatch-through: 17