Remove set-but-not-used variable.

In branches before 9.3, commit 8703059c6 caused join_is_legal()'s
unique_ified variable to become unused, since its only remaining
use is for LATERAL-related tests which don't exist pre-9.3.
My compiler didn't complain about that, but Peter's does.

src/backend/optimizer/path/joinrels.c

@@ -324,7 +324,6 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 {
 	SpecialJoinInfo *match_sjinfo;
 	bool		reversed;
-	bool		unique_ified;
 	bool		must_be_leftjoin;
 	ListCell   *l;
 
@@ -342,7 +341,6 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 	 */
 	match_sjinfo = NULL;
 	reversed = false;
-	unique_ified = false;
 	must_be_leftjoin = false;
 
 	foreach(l, root->join_info_list)
@@ -444,7 +442,6 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 				return false;	/* invalid join path */
 			match_sjinfo = sjinfo;
 			reversed = false;
-			unique_ified = true;
 		}
 		else if (sjinfo->jointype == JOIN_SEMI &&
 				 bms_equal(sjinfo->syn_righthand, rel1->relids) &&
@@ -456,7 +453,6 @@ join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 				return false;	/* invalid join path */
 			match_sjinfo = sjinfo;
 			reversed = true;
-			unique_ified = true;
 		}
 		else
 		{