Fix bogus comments

Alvaro Herrera <alvherre@alvh.no-ip.org>

Commit: 4140619df909ed90f485c0e96a5c4b901e544976
Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2016-05-12T19:02:49Z
Releases: 9.5.4
Fix bogus comments

Some comments mentioned XLogReplayBuffer, but there's no such function:
that was an interim name for a function that got renamed to
XLogReadBufferForRedo, before commit 2c03216d831160 was pushed.

Files