Improve code comments

As of 0c2c81b4, the replication
parameter in libpq is no longer "deliberately undocumented".

src/backend/replication/libpqwalreceiver/libpqwalreceiver.c

@@ -128,10 +128,7 @@ libpqrcv_connect(const char *conninfo, bool logical, const char *appname,
 
 	/*
 	 * We use the expand_dbname parameter to process the connection string (or
-	 * URI), and pass some extra options. The deliberately undocumented
-	 * parameter "replication=true" makes it a replication connection. The
-	 * database name is ignored by the server in replication mode, but specify
-	 * "replication" for .pgpass lookup.
+	 * URI), and pass some extra options.
 	 */
 	keys[i] = "dbname";
 	vals[i] = conninfo;
@@ -139,6 +136,10 @@ libpqrcv_connect(const char *conninfo, bool logical, const char *appname,
 	vals[i] = logical ? "database" : "true";
 	if (!logical)
 	{
+		/*
+		 * The database name is ignored by the server in replication mode, but
+		 * specify "replication" for .pgpass lookup.
+		 */
 		keys[++i] = "dbname";
 		vals[i] = "replication";
 	}