Silence "missing contrecord" error.

Silence "missing contrecord" error.

Commit dd38ff28ad added a new error message "missing contrecord" when
we fail to reassemble a record.  Unfortunately that caused noisy
messages to be logged by pg_waldump at end of segment, and by walsender
when asked to shut down on a segment boundary.

Remove the new error message, so that this condition signals end-of-
WAL without a message.  It's arguably a reportable condition that should
not be silenced while performing crash recovery, but fixing that without
introducing noise in the other cases will require more research.

Back-patch to 15.

Reported-by: Tomas Vondra <tomas.vondra@enterprisedb.com>
Discussion: https://postgr.es/m/6a1df56e-4656-b3ce-4b7a-a9cb41df8189%40enterprisedb.com