Remove discrete inputs from openmdao wrapper

[dzalkind]

Purpose

Discrete inputs to RAFT openmdao wrapper were making it difficult to use optimization routines that use finite differencing. All the discrete inputs were changed to modeling options.

Type of change

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

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Checklist

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• I have run existing tests which pass locally with my changes
• I have added new tests or examples that prove my fix is effective or that my feature works
• I have added necessary documentation