MDEV-27648 fixup: delete unused member of st_spider_transaction

st_spider_transaction::thd_hash_value is no longer used because of
MDEV-27648.

storage/spider/spd_include.h

@@ -636,7 +636,6 @@ typedef struct st_spider_transaction
   bool               updated_in_this_trx;
 
   THD                *thd;
-  my_hash_value_type thd_hash_value;
   XID                xid;
   HASH               trx_conn_hash;
   uint               trx_conn_hash_id;

storage/spider/spd_trx.cc

@@ -1247,11 +1247,6 @@ SPIDER_TRX *spider_get_trx(
       trx->trx_ha_hash.array.size_of_element);
 
     trx->thd = (THD*) thd;
-    if (thd)
-      trx->thd_hash_value = my_calc_hash(&spider_allocated_thds,
-        (uchar*) thd, sizeof(THD *));
-    else
-      trx->thd_hash_value = 0;
     pthread_mutex_lock(&spider_thread_id_mutex);
     trx->spider_thread_id = spider_thread_id;
     ++spider_thread_id;