Remove walredo-related hacks from InternalIpcMemoryCreate()

Now similar kind of hack (using malloc() instead of shmem) is
done in the wal-redo extension.

Author: kelvich

src/backend/port/sysv_shmem.c

@@ -155,22 +155,6 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
 		}
 	}
 #endif
-
-	/*
-	 * NEON: do not create shared memory segments for single user wal redo
-	 * postgres. Many spawned instances of wal redo may exhaust kernel.shmmni
-	 */
-	if (am_wal_redo_postgres)
-	{
-		void	   *ptr = malloc(size);
-
-		if (ptr == NULL)
-		{
-			ereport(FATAL,
-					(errmsg("could not create shared memory segment with size %zu for WAL redo process", size)));
-		}
-		return ptr;
-	}
 	shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);
 
 	if (shmid < 0)