Revert "Doc: mention that reloading is not necessary when pool_passwd is updated."

Revert "Doc: mention that reloading is not necessary when pool_passwd is updated."

This reverts commit 4695affe7859338fa41d860dac74bfbebea7a88a.

"reloading is not necessary when pool_passwd is updated." was not
correct. Since reading pool_passwd in pgpool uses a buffered read,
it's too fragile to assume that changes to pool_passwd by different
process is immediately available for pgpool process. To reflect the
changes, pgpool reload (which causes re-opening pool_passwd). is
necessary.

Discussion: [pgpool-general: 9185] reloading of pool_passwd file
https://www.pgpool.net/pipermail/pgpool-general/2024-August/001862.html