main-loop: drop spin_counter

main-loop: drop spin_counter

Commit d759c951f3287fad04210a52f2dc93f94cf58c7f ("replay: push
replay_mutex_lock up the call tree") removed the !timeout lock
optimization in the main loop.

The idea of the optimization was to avoid ping-pongs between threads by
keeping the Big QEMU Lock held across non-blocking (!timeout) main loop
iterations.

A warning is printed when the main loop spins without releasing BQL for
long periods of time.  These warnings were supposed to aid debugging but
in practice they just alarm users.  They are considered noise because
the cause of spinning is not shown and is hard to find.

Now that the lock optimization has been removed, there is no danger of
hogging the BQL.  Drop the spin counter and the infamous warning.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>