Updated and added new versions to the METIS/ParMETIS packages.

- Added a 'url_for_version' function to the METIS/ParMETIS packages.
- Added installation support for METIS@5.0.2 and ParMETIS@4.0.2.
- Changed the 'double' variant to 'real64' to make it more consistent
  with the 'idx64' variant naming.
- Removed an unnecessary dependency on gdb.