Remove now-dead code in StoreAttrDefault().

StoreAttrDefault() is no longer responsible for filling
attmissingval, so remove the code for that.

Get rid of RawColumnDefault.missingMode, too, as we no longer
need that to pass information around.

While here, clean up some sloppy coding in StoreAttrDefault(),
such as failure to use XXXGetDatum macros.  These aren't bugs
but they're not good code either.

Reported-by: jian he <jian.universality@gmail.com>
Author: jian he <jian.universality@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CACJufxHFssPvkP1we7WMhPD_1kwgbG52o=kQgL+TnVoX5LOyCQ@mail.gmail.com

src/include/catalog/heap.h

@@ -29,7 +29,6 @@ typedef struct RawColumnDefault
 {
 	AttrNumber	attnum;			/* attribute to attach default to */
 	Node	   *raw_default;	/* default value (untransformed parse tree) */
-	bool		missingMode;	/* obsolete, no longer used */
 	char		generated;		/* attgenerated setting */
 } RawColumnDefault;
 

src/include/catalog/pg_attrdef.h

@@ -57,8 +57,7 @@ DECLARE_FOREIGN_KEY((adrelid, adnum), pg_attribute, (attrelid, attnum));
 
 
 extern Oid	StoreAttrDefault(Relation rel, AttrNumber attnum,
-							 Node *expr, bool is_internal,
-							 bool add_column_mode);
+							 Node *expr, bool is_internal);
 extern void RemoveAttrDefault(Oid relid, AttrNumber attnum,
 							  DropBehavior behavior,
 							  bool complain, bool internal);