Fix outdated comments in slru.c

SlruRecentlyUsed() is an inline function since 53c2a97a92, not a
macro.  The description of long_segment_names was missing at the top of
SimpleLruInit(), part forgotten in 4ed8f0913b.

Author: Julien Rouhaud <rjuju123@gmail.com>
Discussion: https://postgr.es/m/aLpBLMOYwEQkaleF@jrouhaud
Backpatch-through: 17

src/backend/access/transam/slru.c

@@ -246,6 +246,7 @@ SimpleLruAutotuneBuffers(int divisor, int max)
  * buffer_tranche_id: tranche ID to use for the SLRU's per-buffer LWLocks.
  * bank_tranche_id: tranche ID to use for the bank LWLocks.
  * sync_handler: which set of functions to use to handle sync requests
+ * long_segment_names: use short or long segment names
  */
 void
 SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
@@ -644,7 +645,7 @@ SimpleLruReadPage_ReadOnly(SlruCtl ctl, int64 pageno, TransactionId xid)
 			shared->page_number[slotno] == pageno &&
 			shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS)
 		{
-			/* See comments for SlruRecentlyUsed macro */
+			/* See comments for SlruRecentlyUsed() */
 			SlruRecentlyUsed(shared, slotno);
 
 			/* update the stats counter of pages found in the SLRU */