Fix comment of SimpleLruInit() in slru.c
sync_handler was not mentioned in the comment block of the function.
Oversight in
dee663f.
Author: Aleksander Alekseev
Discussion: https://postgr.es/m/CAJ7c6TPUd9BwNY47TtMxaijLHSbyHNdhu=kvbGnvO_bi+oC6_Q@mail.gmail.com
Backpatch-through: 14