Remove no-longer-needed fields of Hash plan nodes.

skewColType/skewColTypmod are no longer used in the wake of commit
9aab83fc, and seem unlikely to be wanted in future, so let's drop 'em.

Discussion: https://postgr.es/m/16364.1494520862@sss.pgh.pa.us

src/backend/nodes/copyfuncs.c

@@ -1052,8 +1052,6 @@ _copyHash(const Hash *from)
 	COPY_SCALAR_FIELD(skewTable);
 	COPY_SCALAR_FIELD(skewColumn);
 	COPY_SCALAR_FIELD(skewInherit);
-	COPY_SCALAR_FIELD(skewColType);
-	COPY_SCALAR_FIELD(skewColTypmod);
 
 	return newnode;
 }

src/backend/nodes/outfuncs.c

@@ -898,8 +898,6 @@ _outHash(StringInfo str, const Hash *node)
 	WRITE_OID_FIELD(skewTable);
 	WRITE_INT_FIELD(skewColumn);
 	WRITE_BOOL_FIELD(skewInherit);
-	WRITE_OID_FIELD(skewColType);
-	WRITE_INT_FIELD(skewColTypmod);
 }
 
 static void

src/backend/nodes/readfuncs.c

@@ -2187,8 +2187,6 @@ _readHash(void)
 	READ_OID_FIELD(skewTable);
 	READ_INT_FIELD(skewColumn);
 	READ_BOOL_FIELD(skewInherit);
-	READ_OID_FIELD(skewColType);
-	READ_INT_FIELD(skewColTypmod);
 
 	READ_DONE();
 }

src/backend/optimizer/plan/createplan.c

@@ -224,9 +224,7 @@ static HashJoin *make_hashjoin(List *tlist,
 static Hash *make_hash(Plan *lefttree,
 		  Oid skewTable,
 		  AttrNumber skewColumn,
-		  bool skewInherit,
-		  Oid skewColType,
-		  int32 skewColTypmod);
+		  bool skewInherit);
 static MergeJoin *make_mergejoin(List *tlist,
 			   List *joinclauses, List *otherclauses,
 			   List *mergeclauses,
@@ -4065,8 +4063,6 @@ create_hashjoin_plan(PlannerInfo *root,
 	Oid			skewTable = InvalidOid;
 	AttrNumber	skewColumn = InvalidAttrNumber;
 	bool		skewInherit = false;
-	Oid			skewColType = InvalidOid;
-	int32		skewColTypmod = -1;
 
 	/*
 	 * HashJoin can project, so we don't have to demand exact tlists from the
@@ -4153,8 +4149,6 @@ create_hashjoin_plan(PlannerInfo *root,
 				skewTable = rte->relid;
 				skewColumn = var->varattno;
 				skewInherit = rte->inh;
-				skewColType = var->vartype;
-				skewColTypmod = var->vartypmod;
 			}
 		}
 	}
@@ -4165,9 +4159,7 @@ create_hashjoin_plan(PlannerInfo *root,
 	hash_plan = make_hash(inner_plan,
 						  skewTable,
 						  skewColumn,
-						  skewInherit,
-						  skewColType,
-						  skewColTypmod);
+						  skewInherit);
 
 	/*
 	 * Set Hash node's startup & total costs equal to total cost of input
@@ -5427,9 +5419,7 @@ static Hash *
 make_hash(Plan *lefttree,
 		  Oid skewTable,
 		  AttrNumber skewColumn,
-		  bool skewInherit,
-		  Oid skewColType,
-		  int32 skewColTypmod)
+		  bool skewInherit)
 {
 	Hash	   *node = makeNode(Hash);
 	Plan	   *plan = &node->plan;
@@ -5442,8 +5432,6 @@ make_hash(Plan *lefttree,
 	node->skewTable = skewTable;
 	node->skewColumn = skewColumn;
 	node->skewInherit = skewInherit;
-	node->skewColType = skewColType;
-	node->skewColTypmod = skewColTypmod;
 
 	return node;
 }

src/include/nodes/plannodes.h

@@ -858,8 +858,7 @@ typedef struct GatherMerge
  *
  * If the executor is supposed to try to apply skew join optimization, then
  * skewTable/skewColumn/skewInherit identify the outer relation's join key
- * column, from which the relevant MCV statistics can be fetched.  Also, its
- * type information is provided to save a lookup.
+ * column, from which the relevant MCV statistics can be fetched.
  * ----------------
  */
 typedef struct Hash
@@ -868,8 +867,6 @@ typedef struct Hash
 	Oid			skewTable;		/* outer join key's table OID, or InvalidOid */
 	AttrNumber	skewColumn;		/* outer join key's column #, or zero */
 	bool		skewInherit;	/* is outer join rel an inheritance tree? */
-	Oid			skewColType;	/* datatype of the outer key column */
-	int32		skewColTypmod;	/* typmod of the outer key column */
 	/* all other info is in the parent HashJoin node */
 } Hash;