bpo-31653: Remove deadcode in semlock_acquire() (#4091)

Fix the following Coverity warning:

>>>     CID 1420038:  Control flow issues  (DEADCODE)
>>>     Execution cannot reach this statement: "res = sem_trywait(self->han...".
321                     res = sem_trywait(self->handle);

The deadcode was introduced by the commit
c872d39d324cd6f1a71b73e10406bbaed192d35f.