MDEV-7620: Remove the data structures

The instrumentation that was added in
commit 90635c6f (MDEV-7620)
was effectively reverted in MariaDB Server 10.2.2, in
commit 2e814d47
(which stopped reporting the statistics) and
commit fec844ac
(which stopped updating the statistics).

Let us remove the orphan data members to reduce the memory footprint.

storage/innobase/include/trx0trx.h

@@ -1113,20 +1113,6 @@ struct trx_t {
 	during bulk create index */
 	FlushObserver*	flush_observer;
 public:
-	/* Lock wait statistics */
-	ulint		n_rec_lock_waits;
-					/*!< Number of record lock waits,
-					might not be exactly correct. */
-	ulint		n_table_lock_waits;
-					/*!< Number of table lock waits,
-					might not be exactly correct. */
-	ulint		total_rec_lock_wait_time;
-					/*!< Total rec lock wait time up
-					to this moment. */
-	ulint		total_table_lock_wait_time;
-					/*!< Total table lock wait time
-					up to this moment. */
-
 #ifdef WITH_WSREP
 	os_event_t	wsrep_event;	/* event waited for in srv_conc_slot */
 #endif /* WITH_WSREP */

storage/innobase/trx/trx0trx.cc

@@ -464,10 +464,6 @@ inline void trx_t::free()
   MEM_NOACCESS(&mod_tables, sizeof mod_tables);
   MEM_NOACCESS(&detailed_error, sizeof detailed_error);
   MEM_NOACCESS(&flush_observer, sizeof flush_observer);
-  MEM_NOACCESS(&n_rec_lock_waits, sizeof n_rec_lock_waits);
-  MEM_NOACCESS(&n_table_lock_waits, sizeof n_table_lock_waits);
-  MEM_NOACCESS(&total_rec_lock_wait_time, sizeof total_rec_lock_wait_time);
-  MEM_NOACCESS(&total_table_lock_wait_time, sizeof total_table_lock_wait_time);
 #ifdef WITH_WSREP
   MEM_NOACCESS(&wsrep_event, sizeof wsrep_event);
 #endif /* WITH_WSREP */