Use one input param for gravity to avoid inconsistencies

[moprak-nrel]

Summary

We currently have a couple places that read gravity from the input files using ABL.gravity instead of incflo.gravity. I suspect this was a bug since most other places use the latter.

Pull request type

Please check the type of change introduced:

• [x] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Documentation content changes
• [ ] Other (please describe):

Checklist

The following is included:

• [ ] new unit-test(s)
• [ ] new regression test(s)
• [ ] documentation for new capability

This PR was tested by running:

• the unit tests
  • [x] on GPU
  • [x] on CPU
• the regression tests
  • [ ] on GPU
  • [ ] on CPU

None of the regtests use ABL.gravity

Additional background

Issue Number: