Clean-up: removing duplicate code: removing

Item_func_in::compare_collation() and Item_func_between::compare_collation(),
and adding Item_func_opt_neg::compare_collation() instead.

sql/item_cmpfunc.h

@@ -707,6 +707,7 @@ class Item_func_opt_neg :public Item_bool_func
     return this;
   }
   bool eq(const Item *item, bool binary_cmp) const;
+  CHARSET_INFO *compare_collation() const { return cmp_collation.collation; }
   Item* propagate_equal_fields(THD *thd, const Context &ctx, COND_EQUAL *cond)
   {
     Item_args::propagate_equal_fields(thd,
@@ -733,7 +734,6 @@ class Item_func_between :public Item_func_opt_neg
   const char *func_name() const { return "between"; }
   void fix_length_and_dec();
   virtual void print(String *str, enum_query_type query_type);
-  CHARSET_INFO *compare_collation() const { return cmp_collation.collation; }
   bool eval_not_null_tables(uchar *opt_arg);
   void fix_after_pullout(st_select_lex *new_parent, Item **ref);
   bool count_sargable_conds(uchar *arg);
@@ -1396,7 +1396,6 @@ class Item_func_in :public Item_func_opt_neg
   enum Functype functype() const { return IN_FUNC; }
   const char *func_name() const { return " IN "; }
   bool nulls_in_row();
-  CHARSET_INFO *compare_collation() const { return cmp_collation.collation; }
   bool eval_not_null_tables(uchar *opt_arg);
   void fix_after_pullout(st_select_lex *new_parent, Item **ref);
   bool count_sargable_conds(uchar *arg);