gdb: remove TYPE_FIELD macro

Replace all uses of it by type::field.

Note that since type::field returns a reference to the field, some spots
are used to assign the whole field structure.  See ctfread.c, function
attach_fields_to_type, for example.  This is the same as was happening
with the macro, so I don't think it's a problem, but if anybody sees a
really nicer way to do this, now could be a good time to implement it.

gdb/ChangeLog:

	* gdbtypes.h (TYPE_FIELD): Remove.  Replace all uses with
	type::field.

gdb/python/py-type.c

@@ -177,7 +177,7 @@ convert_field (struct type *type, int field)
   if (PyObject_SetAttrString (result.get (), "parent_type", arg.get ()) < 0)
     return NULL;
 
-  if (!field_is_static (&TYPE_FIELD (type, field)))
+  if (!field_is_static (&type->field (field)))
     {
       const char *attrstring;