Reconcile nodes/*funcs.c with PostgreSQL 12 work.

One would have needed out-of-tree code to observe the defects.  Remove
unreferenced fields instead of completing their support functions.
Since in-tree code can't reach _readIntoClause(), no catversion bump.

src/backend/nodes/outfuncs.c

@@ -1048,7 +1048,7 @@ _outIntoClause(StringInfo str, const IntoClause *node)
 
 	WRITE_NODE_FIELD(rel);
 	WRITE_NODE_FIELD(colNames);
-	WRITE_NODE_FIELD(accessMethod);
+	WRITE_STRING_FIELD(accessMethod);
 	WRITE_NODE_FIELD(options);
 	WRITE_ENUM_FIELD(onCommit, OnCommitAction);
 	WRITE_STRING_FIELD(tableSpaceName);

src/backend/parser/parse_node.c

@@ -306,7 +306,6 @@ transformContainerSubscripts(ParseState *pstate,
 	bool		isSlice = false;
 	List	   *upperIndexpr = NIL;
 	List	   *lowerIndexpr = NIL;
-	List	   *indexprSlice = NIL;
 	ListCell   *idx;
 	SubscriptingRef *sbsref;
 
@@ -450,7 +449,6 @@ transformContainerSubscripts(ParseState *pstate,
 	/* refcollid will be set by parse_collate.c */
 	sbsref->refupperindexpr = upperIndexpr;
 	sbsref->reflowerindexpr = lowerIndexpr;
-	sbsref->refindexprslice = indexprSlice;
 	sbsref->refexpr = (Expr *) containerBase;
 	sbsref->refassgnexpr = (Expr *) assignFrom;
 

src/include/nodes/parsenodes.h

@@ -2139,7 +2139,6 @@ typedef struct Constraint
 	Node	   *raw_expr;		/* expr, as untransformed parse tree */
 	char	   *cooked_expr;	/* expr, as nodeToString representation */
 	char		generated_when; /* ALWAYS or BY DEFAULT */
-	char		generated_kind; /* currently always STORED */
 
 	/* Fields used for unique constraints (UNIQUE and PRIMARY KEY): */
 	List	   *keys;			/* String nodes naming referenced key

src/include/nodes/primnodes.h

@@ -410,8 +410,6 @@ typedef struct SubscriptingRef
 	List	   *reflowerindexpr;	/* expressions that evaluate to lower
 									 * container indexes, or NIL for single
 									 * container element */
-	List	   *refindexprslice;	/* whether or not related indexpr from
-									 * reflowerindexpr is a slice */
 	Expr	   *refexpr;		/* the expression that evaluates to a
 								 * container value */