Remove obsolete prohibition on function name matching a column name.

ProcedureCreate formerly threw an error if the function to be created
has one argument of composite type and the function name matches some
column of the composite type.  This was a (very non-bulletproof) defense
against creating situations where f(x) and x.f are ambiguous.  But we
don't really need such a defense in the wake of commit b97a3465, which
allows us to deal with such situations fairly cleanly.  This behavior
also created a dump-and-reload hazard, since a function might be
rejected if a conflicting column name had been added to the input
composite type later.  Hence, let's just drop the check.

Discussion: https://postgr.es/m/CAOW5sYa3Wp7KozCuzjOdw6PiOYPi6D=VvRybtH2S=2C0SVmRmA@mail.gmail.com

src/backend/catalog/pg_proc.c

@@ -108,7 +108,6 @@ ProcedureCreate(const char *procedureName,
 	bool		nulls[Natts_pg_proc];
 	Datum		values[Natts_pg_proc];
 	bool		replaces[Natts_pg_proc];
-	Oid			relid;
 	NameData	procname;
 	TupleDesc	tupDesc;
 	bool		is_update;
@@ -254,20 +253,6 @@ ProcedureCreate(const char *procedureName,
 				 errmsg("unsafe use of pseudo-type \"internal\""),
 				 errdetail("A function returning \"internal\" must have at least one \"internal\" argument.")));
 
-	/*
-	 * don't allow functions of complex types that have the same name as
-	 * existing attributes of the type
-	 */
-	if (parameterCount == 1 &&
-		OidIsValid(parameterTypes->values[0]) &&
-		(relid = typeOrDomainTypeRelid(parameterTypes->values[0])) != InvalidOid &&
-		get_attnum(relid, procedureName) != InvalidAttrNumber)
-		ereport(ERROR,
-				(errcode(ERRCODE_DUPLICATE_COLUMN),
-				 errmsg("\"%s\" is already an attribute of type %s",
-						procedureName,
-						format_type_be(parameterTypes->values[0]))));
-
 	if (paramModes != NULL)
 	{
 		/*