Merge a fix from MySQL 5.7, to presumably dead code

Remove a test that does not apply to MariaDB

In MariaDB, there are no high-priority transactions (no tx_priority).
This should also mean that all references to TRX_STATE_FORCED_ROLLBACK
are dead code.

storage/innobase/lock/lock0lock.cc

 /*****************************************************************************
 
-Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 1996, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2014, 2017, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
@@ -2728,7 +2728,10 @@ RecLock::lock_add_priority(
 	lock_t*	grant_position = NULL;
 	lock_t*	add_position = NULL;
 
-	HASH_SEARCH(hash, lock_sys->rec_hash, m_rec_id.fold(), lock_t*,
+	/* Different lock (such as predicate lock) are on different hash */
+	hash_table_t*	lock_hash = lock_hash_get(m_mode);
+
+	HASH_SEARCH(hash, lock_hash, m_rec_id.fold(), lock_t*,
 		    lock_head, ut_ad(lock_head->is_record_lock()), true);
 
 	ut_ad(lock_head);