Also remove get_last_xlog_replay_timestamp() function and the sql_utils dir,
we can readded later if we need.
We don't need the column last_wal_standby_timestamp in repl_status, so
remove it
and replaced by GetLatestXTime() but this function cannot
be called from external programs.
Instead now we are using GetXLogReceiptTime() which tells
us what was the last time we got a WAL record by streaming
or file.
