This function is only used by xlogreader.c itself, so there's no need to
export it. It was introduced by commit 3b02ea4f0780 with the apparent
intention that it could be used externally, but I couldn't find any
external code calling it.
I (Álvaro) couldn't resist the urge to sort nearby function prototypes
properly while at it.
Author: Antonin Houska
Discussion: https://postgr.es/m/14984.1554998742@spoje.net
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