Replace ITK mutexes with std mutexes

• #include "itkSimpleFastMutexLock.h" -> #include <mutex>
• #include "itkMutexLockHolder.h" -> #include <mutex>
• itk::SimpleFastMutexLock -> std::mutex
• itk::MutexLockHolder<itk::SimpleFastMutexLock> -> std::lock_guard<std::mutex>
• Lock()/Unlock() -> lock()/unlock()