Fix HY_Features_MPI to match feature-type behavior of HY_Features from PR #665

[PhilMiller]

#665 modified HY_Features.cpp to use predicate functions that recognize a broader set of identifier prefixes to describe catchments and nexuses. The corresponding change to the mostly-duplicate code in HY_Features_MPI was not made, so I do that here.

Changes

• Use isCatchment() and isNexus() predicate functions

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

[hellkite500]

I didn't implement this prior due to the refactor I proposed in #668. I haven't had a chance to come back to that, so thanks for putting this in in the mean time.