patch 9.0.1952: Vim9: unused static field

Problem:  Vim9: unused static field
Solution: remove it and simplify code

closes: #13220

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/proto/vim9class.pro b/src/proto/vim9class.pro
index d09f654..9edf354 100644
--- a/src/proto/vim9class.pro
+++ b/src/proto/vim9class.pro
@@ -1,5 +1,5 @@
 /* vim9class.c */
-int object_index_from_itf_index(class_T *itf, int is_method, int idx, class_T *cl, int is_static);
+int object_index_from_itf_index(class_T *itf, int is_method, int idx, class_T *cl);
 void ex_class(exarg_T *eap);
 type_T *class_member_type(class_T *cl, int is_object, char_u *name, char_u *name_end, int *member_idx);
 void ex_enum(exarg_T *eap);