Remove error report from pq_endmessage when pq_putmessage fails. The

Remove error report from pq_endmessage when pq_putmessage fails.  The
only possible failure is in pq_flush, which will log a (better!) report
anyway --- so pq_endmessage is just cluttering the log with a redundant
entry.  This matters when a client crashes partway through a large query,
since we will emit many broken-pipe reports before finishing the query
and exiting.