Remove smgrdounlink() in smgr.c from the code tree

The last caller of this routine was removed in b4166911, and as a wise
man said one day, dead code tends to silently break.

Per discussion between Fujii Masao, Peter Geoghegan, Vignesh C and me.

Reported-by: Peter Geoghegan
Discussion: https://postgr.es/m/CAH2-Wz=sg5H8-vG4d5UmAofdcRMpeTDt2K-NUWp4GSfhenRGAQ@mail.gmail.com

src/backend/storage/smgr/smgr.c

@@ -335,59 +335,6 @@ smgrcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo)
 	smgrsw[reln->smgr_which].smgr_create(reln, forknum, isRedo);
 }
 
-/*
- *	smgrdounlink() -- Immediately unlink all forks of a relation.
- *
- *		All forks of the relation are removed from the store.  This should
- *		not be used during transactional operations, since it can't be undone.
- *
- *		If isRedo is true, it is okay for the underlying file(s) to be gone
- *		already.
- */
-void
-smgrdounlink(SMgrRelation reln, bool isRedo)
-{
-	RelFileNodeBackend rnode = reln->smgr_rnode;
-	int			which = reln->smgr_which;
-	ForkNumber	forknum;
-
-	/* Close the forks at smgr level */
-	for (forknum = 0; forknum <= MAX_FORKNUM; forknum++)
-		smgrsw[which].smgr_close(reln, forknum);
-
-	/*
-	 * Get rid of any remaining buffers for the relation.  bufmgr will just
-	 * drop them without bothering to write the contents.
-	 */
-	DropRelFileNodesAllBuffers(&rnode, 1);
-
-	/*
-	 * It'd be nice to tell the stats collector to forget it immediately, too.
-	 * But we can't because we don't know the OID (and in cases involving
-	 * relfilenode swaps, it's not always clear which table OID to forget,
-	 * anyway).
-	 */
-
-	/*
-	 * Send a shared-inval message to force other backends to close any
-	 * dangling smgr references they may have for this rel.  We should do this
-	 * before starting the actual unlinking, in case we fail partway through
-	 * that step.  Note that the sinval message will eventually come back to
-	 * this backend, too, and thereby provide a backstop that we closed our
-	 * own smgr rel.
-	 */
-	CacheInvalidateSmgr(rnode);
-
-	/*
-	 * Delete the physical file(s).
-	 *
-	 * Note: smgr_unlink must treat deletion failure as a WARNING, not an
-	 * ERROR, because we've already decided to commit or abort the current
-	 * xact.
-	 */
-	smgrsw[which].smgr_unlink(rnode, InvalidForkNumber, isRedo);
-}
-
 /*
  *	smgrdosyncall() -- Immediately sync all forks of all given relations
  *
@@ -432,9 +379,6 @@ smgrdosyncall(SMgrRelation *rels, int nrels)
  *
  *		If isRedo is true, it is okay for the underlying file(s) to be gone
  *		already.
- *
- *		This is equivalent to calling smgrdounlink for each relation, but it's
- *		significantly quicker so should be preferred when possible.
  */
 void
 smgrdounlinkall(SMgrRelation *rels, int nrels, bool isRedo)

src/include/storage/smgr.h

@@ -88,7 +88,6 @@ extern void smgrclose(SMgrRelation reln);
 extern void smgrcloseall(void);
 extern void smgrclosenode(RelFileNodeBackend rnode);
 extern void smgrcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo);
-extern void smgrdounlink(SMgrRelation reln, bool isRedo);
 extern void smgrdosyncall(SMgrRelation *rels, int nrels);
 extern void smgrdounlinkall(SMgrRelation *rels, int nrels, bool isRedo);
 extern void smgrextend(SMgrRelation reln, ForkNumber forknum,