cleanup: remove redundant ADDINTERVAL_PRECEDENCE

expression between INTERVAL and the unit doesns not need any
precedence rules, there's no ambiguity there

sql/item.h

@@ -87,7 +87,7 @@ enum precedence {
   BITOR_PRECEDENCE,     // |
   BITAND_PRECEDENCE,    // &
   SHIFT_PRECEDENCE,     // <<, >>
-  ADDINTERVAL_PRECEDENCE, // first argument in +INTERVAL
+  INTERVAL_PRECEDENCE,  // first argument in +INTERVAL
   ADD_PRECEDENCE,       // +, -
   MUL_PRECEDENCE,       // *, /, DIV, %, MOD
   BITXOR_PRECEDENCE,    // ^
@@ -95,7 +95,6 @@ enum precedence {
   NEG_PRECEDENCE,       // unary -, ~
   BANG_PRECEDENCE,      // !, NOT (if HIGH_NOT_PRECEDENCE)
   COLLATE_PRECEDENCE,   // BINARY, COLLATE
-  INTERVAL_PRECEDENCE,  // INTERVAL
   DEFAULT_PRECEDENCE,
   HIGHEST_PRECEDENCE
 };

sql/item_timefunc.cc

@@ -2250,9 +2250,9 @@ static const char *interval_names[]=
 
 void Item_date_add_interval::print(String *str, enum_query_type query_type)
 {
-  args[0]->print_parenthesised(str, query_type, ADDINTERVAL_PRECEDENCE);
+  args[0]->print_parenthesised(str, query_type, INTERVAL_PRECEDENCE);
   str->append(date_sub_interval?" - interval ":" + interval ");
-  args[1]->print_parenthesised(str, query_type, INTERVAL_PRECEDENCE);
+  args[1]->print(str, query_type);
   str->append(' ');
   str->append(interval_names[int_type]);
 }

sql/item_timefunc.h

@@ -942,7 +942,7 @@ class Item_date_add_interval :public Item_temporal_hybrid_func
   bool get_date(MYSQL_TIME *res, ulonglong fuzzy_date);
   bool eq(const Item *item, bool binary_cmp) const;
   void print(String *str, enum_query_type query_type);
-  enum precedence precedence() const { return ADDINTERVAL_PRECEDENCE; }
+  enum precedence precedence() const { return INTERVAL_PRECEDENCE; }
   bool need_parentheses_in_default() { return true; }
   Item *get_copy(THD *thd, MEM_ROOT *mem_root)
   { return get_item_copy<Item_date_add_interval>(thd, mem_root, this); }