Clean up Monitor::_safepoint_check usage to Mutex::_safepoint_check

From code review comments from [~rehn]: First, a side note, I notice that we forgot to change, e.g.:
Monitor::_safepoint_check_never to Mutex::_safepoint_check_never in some places.

I'd left Monitor::_safepoint_check_never in places where the code had new Monitor(etc, Monitor::_safepoint_check_never); ie. the code was initializing a Monitor. But there are some left over from allocating a Mutex. The code for mutexLocker.cpp that initializes the mutex/monitors doesn't need to specify Monitor::_safepoint_check_{never,sometimes,always}. It can be done in the macro.