Remove dead code in pg_ctl.c.

Missed in 39969e2a1e.

Author: David Steele
Discussion: https://postgr.es/m/0c742f0c-d663-419d-b5a7-4fe867f5566c%40pgmasters.net

src/bin/pg_ctl/pg_ctl.c

@@ -96,7 +96,6 @@ static time_t start_time;
 static char postopts_file[MAXPGPATH];
 static char version_file[MAXPGPATH];
 static char pid_file[MAXPGPATH];
-static char backup_file[MAXPGPATH];
 static char promote_file[MAXPGPATH];
 static char logrotate_file[MAXPGPATH];
 
@@ -2447,7 +2446,6 @@ main(int argc, char **argv)
 		snprintf(postopts_file, MAXPGPATH, "%s/postmaster.opts", pg_data);
 		snprintf(version_file, MAXPGPATH, "%s/PG_VERSION", pg_data);
 		snprintf(pid_file, MAXPGPATH, "%s/postmaster.pid", pg_data);
-		snprintf(backup_file, MAXPGPATH, "%s/backup_label", pg_data);
 
 		/*
 		 * Set mask based on PGDATA permissions,