This reverts commit d32ff4ff.
The code around suspending and resuming threads is rather convoluted.
In particular, que_thr_stop_for_mysql() and
lock_wait_suspend_thread() are separated from each other,
and the trx->mutex is being acquired and released multiple times
while a lock wait is being registered. Also, there are multiple
state fields related to lock waits, both in que_thr_t and trx_t.