Fix memqcache_stats_start_time shown in "show pool_status".

Fix memqcache_stats_start_time shown in "show pool_status".

get_config() uses ctime() to generate printable form of
memqcache_stats_start_time. But it did not take into account that
ctime() adds newline at the end of result. As a result, not only the
output of memqcache_stats_start_time was with unnecessary newline but
next row printed empty items.

Author: Tatsuo Ishii <ishii@postgresql.org>
Discussion: https://www.postgresql.org/message-id/20251130.102712.131456481338876013.ishii%40postgresql.org
Backpatch-through: v4.3