Remove the obsolete WITH clause of CREATE FUNCTION.

This clause was superseded by SQL-standard syntax back in 7.3.
We've kept it around for backwards-compatibility purposes ever since;
but 15 years seems like long enough for that, especially seeing that
there are undocumented weirdnesses in how it interacts with the
SQL-standard syntax for specifying the same options.

Michael Paquier, per an observation by Daniel Gustafsson;
some small cosmetic adjustments to nearby code by me.

Discussion: https://postgr.es/m/20180115022748.GB1724@paquier.xyz

src/include/nodes/parsenodes.h

@@ -2735,13 +2735,12 @@ typedef struct CreateStatsStmt
 typedef struct CreateFunctionStmt
 {
 	NodeTag		type;
+	bool		is_procedure;	/* it's really CREATE PROCEDURE */
 	bool		replace;		/* T => replace if already exists */
 	List	   *funcname;		/* qualified name of function to create */
 	List	   *parameters;		/* a list of FunctionParameter */
 	TypeName   *returnType;		/* the return type */
-	bool		is_procedure;
 	List	   *options;		/* a list of DefElem */
-	List	   *withClause;		/* a list of DefElem */
 } CreateFunctionStmt;
 
 typedef enum FunctionParameterMode