#570: Remove 'uses_forcing_file' and 'forcing_file'(_path)

[PhilMiller]

Fix #570 by removing support for unimplemented legacy parameters used to configure forcings inputs.

Removals

• Bmi_Adapter: delete uses_forcing_file and forcing_file (path) members, construction arguments, and accessors
• BMI Formulation classes: stop passing forcing_file arguments through to BMI Adapter classes

Changes

• Delete all forcing_file keys in JSON built in test fixtures
• Throw errors on affirmative use of the never-active and now-removed configuration options

Testing

1. ctest
2. CI

Notes

• There may be documentation that should evolve in tandem
• Users with legacy realization configs may start to see errors related to this. They've already almost certainly added the right options, since otherwise their runs just wouldn't work. So, fixing things is just a matter of removing the old bits from their files.

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 ➡️