Fix redundancy in error messages

pg_log_error() already prints the program name, so we don't need to
print it again inside the message.

src/bin/pg_combinebackup/pg_combinebackup.c

@@ -212,7 +212,7 @@ main(int argc, char *argv[])
 
 	if (optind >= argc)
 	{
-		pg_log_error("%s: no input directories specified", progname);
+		pg_log_error("no input directories specified");
 		pg_log_error_hint("Try \"%s --help\" for more information.", progname);
 		exit(1);
 	}

src/bin/pg_walsummary/pg_walsummary.c

@@ -91,7 +91,7 @@ main(int argc, char *argv[])
 
 	if (optind >= argc)
 	{
-		pg_log_error("%s: no input files specified", progname);
+		pg_log_error("no input files specified");
 		pg_log_error_hint("Try \"%s --help\" for more information.", progname);
 		exit(1);
 	}