Remove perl switch statement and dependency

Old versions of perl supported a switch statement that was later split off into an extension module, and whose use is somewhat discouraged (if not deprecated altogether): https://www.perlmonks.org/?node_id=1167020

The Switch module isn't in the default conda distribution, so it's cumbersome for conda users to install.

This change removes the switch statement from the few places in advligorts that it was used (parameter parsing and tests), replacing it with an if/elsif/else construction.