kconfig: remove unused expr_is_no()

This has not been used since commit e9115030 ("Kconfig: Remove
bad inference rules expr_eliminate_dups2()").
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/kconfig/expr.h

@@ -302,11 +302,6 @@ static inline int expr_is_yes(struct expr *e)
 	return !e || (e->type == E_SYMBOL && e->left.sym == &symbol_yes);
 }
 
-static inline int expr_is_no(struct expr *e)
-{
-	return e && (e->type == E_SYMBOL && e->left.sym == &symbol_no);
-}
-
 #ifdef __cplusplus
 }
 #endif