Remove useless picksplit-doesn't-support-secondary-split log spam.

This LOG message was put in over five years ago with the evident
expectation that we'd make all GiST opclasses support secondary split
directly.  However, no such thing ever happened, and indeed the number of
opclasses supporting it decreased to zero in 9.2.  The reason is that
improving on the default implementation isn't that easy --- the
opclass-specific code that did exist, before 9.2, doesn't appear to have
been any improvement over the default.

Hence, remove the message altogether.  There's certainly no point in
nagging users about this in released branches, but I doubt that we'll
ever implement complete opclass-specific support anyway.

src/backend/access/gist/gistsplit.c

@@ -460,11 +460,6 @@ gistUserPicksplit(Relation r, GistEntryVector *entryvec, int attno, GistSplitVec
 
 		/* Do a generic split */
 		genericPickSplit(giststate, entryvec, sv, attno);
-
-		/* Clean up if we're in a secondary split */
-		if (sv->spl_ldatum_exists || sv->spl_rdatum_exists)
-			supportSecondarySplit(r, giststate, attno, sv,
-								  v->spl_lattr[attno], v->spl_rattr[attno]);
 	}
 	else
 	{
@@ -473,18 +468,13 @@ gistUserPicksplit(Relation r, GistEntryVector *entryvec, int attno, GistSplitVec
 			sv->spl_left[sv->spl_nleft - 1] = (OffsetNumber) (entryvec->n - 1);
 		if (sv->spl_right[sv->spl_nright - 1] == InvalidOffsetNumber)
 			sv->spl_right[sv->spl_nright - 1] = (OffsetNumber) (entryvec->n - 1);
-
-		/* Clean up if we're in a secondary split */
-		if (sv->spl_ldatum_exists || sv->spl_rdatum_exists)
-		{
-			elog(LOG, "picksplit method for column %d of index \"%s\" doesn't support secondary split",
-				 attno + 1, RelationGetRelationName(r));
-
-			supportSecondarySplit(r, giststate, attno, sv,
-								  v->spl_lattr[attno], v->spl_rattr[attno]);
-		}
 	}
 
+	/* Clean up if PickSplit didn't take care of a secondary split */
+	if (sv->spl_ldatum_exists || sv->spl_rdatum_exists)
+		supportSecondarySplit(r, giststate, attno, sv,
+							  v->spl_lattr[attno], v->spl_rattr[attno]);
+
 	/* emit union datums computed by PickSplit back to v arrays */
 	v->spl_lattr[attno] = sv->spl_ldatum;
 	v->spl_rattr[attno] = sv->spl_rdatum;