Remove thread affinity and critical region stuff for Unix

Remove thread affinity and critical region stuff for Unix

The WaitHandleNative::CorWaitMultipleNative was calling Thread::BeginThreadAffinityAndCriticalRegion
that results in incrementing the Thread::m_dwCriticalRegionCount. However, there is nothing
that would decrement it on CoreCLR, so if the WaitHandleNative::CorWaitMultipleNative is called,
in debug build we get an assert in Thread::InternalReset.

It turns out that the critical region and thread affinity stuff is not to be used in CoreCLR,
so I have disabled handling of that in CoreCLR for Unix.
The only remainder are the static methods Thread::BeginThreadAffinity and Thread::EndThreadAffinity
which are used in the ThreadAffinityHolder. Conditionally removing the holder usage would be messy,
so I have rather kept those methods and made their bodies empty.