timer: remove replay clock probe in deadline calculation

Ciro Santilli reported that commit a5ed3525
breaks the execution replay. It happens due to the probing the clock
for the new instances of iothread.
However, this probing was made in replay mode for the timer lists that
are empty.
This patch removes clock probing in replay mode.
It is an artifact of the old version with another thread model.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Message-Id: <20180725121526.12867.17866.stgit@pasha-VirtualBox>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>