MDEV-6247 post-fix: Re-enable some debug assertions

These assertions were disabled in MariaDB 10.1.1 in
commit df4dd593
with a bogus comment referring to the function wsrep_fake_trx_id()
that was introduced in the very same commit.

storage/innobase/include/trx0sys.ic

@@ -445,10 +445,7 @@ trx_id_t
 trx_sys_get_new_trx_id(void)
 /*========================*/
 {
-#ifndef WITH_WSREP
-	/* wsrep_fake_trx_id  violates this assert */
 	ut_ad(mutex_own(&trx_sys->mutex));
-#endif /* WITH_WSREP */
 
 	/* VERY important: after the database is started, max_trx_id value is
 	divisible by TRX_SYS_TRX_ID_WRITE_MARGIN, and the following if

storage/innobase/trx/trx0sys.cc

@@ -180,12 +180,7 @@ trx_sys_flush_max_trx_id(void)
 	mtr_t		mtr;
 	trx_sysf_t*	sys_header;
 
-#ifndef WITH_WSREP
-       /* wsrep_fake_trx_id  violates this assert
-        * Copied from trx_sys_get_new_trx_id
-        */
 	ut_ad(mutex_own(&trx_sys->mutex));
-#endif /* WITH_WSREP */
 
 	if (!srv_read_only_mode) {
 		mtr_start(&mtr);

storage/xtradb/include/trx0sys.ic

@@ -474,10 +474,7 @@ trx_id_t
 trx_sys_get_new_trx_id(void)
 /*========================*/
 {
-#ifndef WITH_WSREP
-	/* wsrep_fake_trx_id  violates this assert */
 	ut_ad(mutex_own(&trx_sys->mutex));
-#endif /* WITH_WSREP */
 
 	/* VERY important: after the database is started, max_trx_id value is
 	divisible by TRX_SYS_TRX_ID_WRITE_MARGIN, and the following if

storage/xtradb/trx/trx0sys.cc

@@ -184,12 +184,7 @@ trx_sys_flush_max_trx_id(void)
 	mtr_t		mtr;
 	trx_sysf_t*	sys_header;
 
-#ifndef WITH_WSREP
-       /* wsrep_fake_trx_id  violates this assert
-        * Copied from trx_sys_get_new_trx_id
-        */
 	ut_ad(mutex_own(&trx_sys->mutex));
-#endif /* WITH_WSREP */
 
 	if (!srv_read_only_mode) {
 		mtr_start(&mtr);