Revert "Fixed: crash trying to 'test_monitor' on Windows(x64)"

From #114
Sorry to bother you.

> Disabling OpenMP, the test was passed.
> I'm going to revert. It should be another issue.
>
> <a href="http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=21719">ImageMagick • View topic - Disabling openMP in windows server</a>