Kernel: Use Vector::unstable_remove() when deallocating a region

Process::m_regions is not sorted, so we can use unstable_remove()
to avoid shifting the vector contents. :^)

Kernel/Process.cpp

@@ -257,7 +257,7 @@ bool Process::deallocate_region(Region& region)
  m_region_lookup_cache.region = nullptr;
  for (int i = 0; i < m_regions.size(); ++i) {
  if (&m_regions[i] == &region) {
- m_regions.remove(i);
+ m_regions.unstable_remove(i);
  return true;
  }
  }