patch 9.0.1822: Vim9: no check for duplicate members in extended classes

Problem:  Vim9: no check for duplicate members in extended classes
Solution: Check for duplicate members in extended classes.
          Fix memory leak.

closes: #12948

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/errors.h b/src/errors.h
index 1ea2460..24977c4 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3487,8 +3487,6 @@
 EXTERN char e_cannot_access_private_method_str[]
 	INIT(= N_("E1366: Cannot access private method: %s"));
 
-EXTERN char e_interface_str_and_class_str_function_access_not_same[]
-	INIT(= N_("E1367: Access type of class method %s differs from interface method %s"));
 EXTERN char e_static_cannot_be_followed_by_this[]
 	INIT(= N_("E1368: Static cannot be followed by \"this\" in a member name"));
 EXTERN char e_duplicate_member_str[]
@@ -3512,4 +3510,4 @@
 EXTERN char e_method_str_type_mismatch_expected_str_but_got_str[]
 	INIT(= N_("E1407: Member \"%s\": type mismatch, expected %s but got %s"));
 
-// E1371 - E1399 unused
+// E1367, E1371 - E1399 unused