Remove trace_recovery_messages

This GUC was intended as a debugging help in the 9.0 area when hot
standby and streaming replication were being developped, able to offer
more information at LOG level rather than DEBUGn.  There are more tools
available these days that are able to offer rather equivalent
information, like pg_waldump introduced in 9.3.  It is not obvious how
this facility is useful these days, so let's remove it.

Author: Bharath Rupireddy
Discussion: https://postgr.es/m/ZXEXEAUVFrvpquSd@paquier.xyz

src/backend/utils/error/elog.c

@@ -3759,29 +3759,3 @@ write_stderr_signal_safe(const char *str)
 		nwritten += rc;
 	}
 }
-
-
-/*
- * Adjust the level of a recovery-related message per trace_recovery_messages.
- *
- * The argument is the default log level of the message, eg, DEBUG2.  (This
- * should only be applied to DEBUGn log messages, otherwise it's a no-op.)
- * If the level is >= trace_recovery_messages, we return LOG, causing the
- * message to be logged unconditionally (for most settings of
- * log_min_messages).  Otherwise, we return the argument unchanged.
- * The message will then be shown based on the setting of log_min_messages.
- *
- * Intention is to keep this for at least the whole of the 9.0 production
- * release, so we can more easily diagnose production problems in the field.
- * It should go away eventually, though, because it's an ugly and
- * hard-to-explain kluge.
- */
-int
-trace_recovery(int trace_level)
-{
-	if (trace_level < LOG &&
-		trace_level >= trace_recovery_messages)
-		return LOG;
-
-	return trace_level;
-}