Accidental revert of MDEV-6933

Commit 2e814d4 merges InnoDB 5.7 from mysql-5.7.9, along with other fixes. I believe it also accidentally reverts 7371dfa (MDEV-6933). Specifically, it adds back these two lines in storage/innobase/lock/lock0wait.cc:

/* Wake the lock timeout monitor thread, if it is suspended */

os_event_set(lock_sys->timeout_event);

I couldn't find any reference to a ticket that was explicitly resolved by reverting this, so I presume the cause is an incorrect merge (mysql-5.7.9 still has that code in lock0wait.cc).