Correct TRASH() macro usage

TRASH was mapped to TRASH_FREE and was supposed to be used for memory
that should not be accessed anymore, while TRASH_ALLOC() is to be
used for uninitialized but to-be-used memory.

But sometimes TRASH() was used in the latter sense.

Remove TRASH() macro, always use explicit TRASH_ALLOC() or TRASH_FREE().

sql/sql_show.cc

@@ -2111,7 +2111,7 @@ public:
   }
   static void operator delete(void *ptr __attribute__((unused)),
                               size_t size __attribute__((unused)))
-  { TRASH(ptr, size); }
+  { TRASH_FREE(ptr, size); }
 
   ulong thread_id;
   time_t start_time;