In Parallel collector, both young and old gen grows/shrinks at the high end; the start address (bottom) is fixed at startup. Therefore, methods like `resize_covered_region_by_end`, used for adjusting the starting address based on `end`, are not needed.

After removing it, one can see `PSCardTable` effectively calls the methods in the base class for resizing regions, so `resize_covered_region` and `resize_covered_region_by_start` can be remove as well.