cleanup: remove redundant BANG_PRECEDENCE

prefix unary operators don't need to have different precedence,
the syntax unambiguously specifies in what order they apply

mysql-test/r/precedence.result

@@ -8068,7 +8068,7 @@ select !cast(1 as char charset binary) AS `! BINARY 1`,cast(!1 as char charset b
 create or replace view v1 as select ! ~ 1, ~ ! 1;
 Select view_definition from information_schema.views where table_schema='test' and table_name='v1';
 view_definition
-select !(~1) AS `! ~ 1`,~!1 AS `~ ! 1`
+select !~1 AS `! ~ 1`,~!1 AS `~ ! 1`
 create or replace view v1 as select - BINARY 1, BINARY - 1;
 Select view_definition from information_schema.views where table_schema='test' and table_name='v1';
 view_definition

sql/item.h

@@ -92,8 +92,7 @@ enum precedence {
   MUL_PRECEDENCE,       // *, /, DIV, %, MOD
   BITXOR_PRECEDENCE,    // ^
   PIPES_PRECEDENCE,     // || (if PIPES_AS_CONCAT)
-  NEG_PRECEDENCE,       // unary -, ~
-  BANG_PRECEDENCE,      // !, NOT (if HIGH_NOT_PRECEDENCE)
+  NEG_PRECEDENCE,       // unary -, ~, !, NOT (if HIGH_NOT_PRECEDENCE)
   COLLATE_PRECEDENCE,   // BINARY, COLLATE
   DEFAULT_PRECEDENCE,
   HIGHEST_PRECEDENCE

sql/item_cmpfunc.h

@@ -574,7 +574,7 @@ class Item_func_not :public Item_bool_func
   longlong val_int();
   enum Functype functype() const { return NOT_FUNC; }
   const char *func_name() const { return "not"; }
-  enum precedence precedence() const { return BANG_PRECEDENCE; }
+  enum precedence precedence() const { return NEG_PRECEDENCE; }
   Item *neg_transformer(THD *thd);
   bool fix_fields(THD *, Item **);
   virtual void print(String *str, enum_query_type query_type);