Fix comment for MAX_SIMUL_LWLOCKS.

This comment mentions that pg_buffercache locks all buffer
partitions simultaneously, but it hasn't done so since v10.

Oversight in commit 6e654546fb.

Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/aKTuAHVEuYCUmmIy%40nathan

src/backend/storage/lmgr/lwlock.c

@@ -162,8 +162,7 @@ LWLockPadded *MainLWLockArray = NULL;
 /*
  * We use this structure to keep track of locked LWLocks for release
  * during error recovery.  Normally, only a few will be held at once, but
- * occasionally the number can be much higher; for example, the pg_buffercache
- * extension locks all buffer partitions simultaneously.
+ * occasionally the number can be much higher.
  */
 #define MAX_SIMUL_LWLOCKS	200