Remove dummy_spinlock

It's been unused since 1b468a131bd2 (2015).

src/backend/main/main.c

@@ -288,12 +288,6 @@ startup_hacks(const char *progname)
 		_CrtSetReportFile(_CRT_WARN, _CRTDBG_FILE_STDERR);
 	}
 #endif							/* WIN32 */
-
-	/*
-	 * Initialize dummy_spinlock, in case we are on a platform where we have
-	 * to use the fallback implementation of pg_memory_barrier().
-	 */
-	SpinLockInit(&dummy_spinlock);
 }
 
 

src/backend/storage/lmgr/s_lock.c

@@ -70,8 +70,6 @@ static uint32 local_my_wait_event_info;
 uint32	   *my_wait_event_info = &local_my_wait_event_info;
 #endif
 
-slock_t		dummy_spinlock;
-
 static int	spins_per_delay = DEFAULT_SPINS_PER_DELAY;
 
 

src/include/storage/s_lock.h

@@ -821,7 +821,6 @@ extern int	tas(volatile slock_t *lock);		/* in port/.../tas.s, or
 #define TAS_SPIN(lock)	TAS(lock)
 #endif	 /* TAS_SPIN */
 
-extern PGDLLIMPORT slock_t dummy_spinlock;
 
 /*
  * Platform-independent out-of-line support routines