pgsql: Remove piece of code to zero out minRecoveryPoint when starting

Log Message:
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Remove piece of code to zero out minRecoveryPoint when starting crash
recovery. It's zeroed out whenever a checkpoint is written, so the only
scenario where the removed code did anything is when you kill archive
recovery, remove recovery.conf, and start up the server, so that it goes
into crash recovery instead. That's a "don't do that" scenario, but it
seems better to not clear minRecoveryPoint but instead update it like we
do in archive recovery, which is what will now happen.

Modified Files:
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    pgsql/src/backend/access/transam:
        xlog.c (r1.368 -> r1.369)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlog.c?r1=1.368&r2=1.369)