Remove rm_safe_restartpoint machinery.

Heikki Linnakangas <heikki.linnakangas@iki.fi>

Commit: 59a5ab3f426e74e3f901dc2cf533726bcea08ed2
Author: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: 2014-03-18T20:10:35Z
Releases: 9.4.0
Remove rm_safe_restartpoint machinery.

It is no longer used, none of the resource managers have multi-record
actions that would make it unsafe to perform a restartpoint.

Also don't allow rm_cleanup to write WAL records, it's also no longer
required. Move the call to rm_cleanup routines to make it more symmetric
with rm_startup.

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