Update implementation of some optional arguments in Icepack

[apcraig]

PR checklist

• [X] Short (1 sentence) summary of your PR: Update implementation of some optional arguments in Icepack
• [X] Developer(s): apcraig
• [X] Suggest PR reviewers from list in the column to the right.
• [X] Please copy the PR test results link or provide a summary of testing completed below. Full test suite on cheyenne with 3 compilers with both Icepack, https://github.com/CICE-Consortium/Test-Results/wiki/icepack_by_hash_forks#67c874194a4acdaf09fc756cd679f579fa53060d, and CICE, https://github.com/CICE-Consortium/Test-Results/wiki/cice_by_hash_forks#b946a95ea46096d739b4b0d725d0eab81a53fbee are bit-for-bit.
• How much do the PR code changes differ from the unmodified code?
  • [X] bit for bit
  • [ ] different at roundoff level
  • [ ] more substantial
• Does this PR create or have dependencies on CICE or any other models?
  • [ ] Yes
  • [X] No
• Does this PR add any new test cases?
  • [ ] Yes
  • [X] No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/.)
  • [ ] Yes
  • [X] No, does the documentation need to be updated at a later time?
    • [ ] Yes
    • [X] No
• [X] Please provide any additional information or relevant details below:

Remove local copies where possible

Check optional arguments

Remove public interface declarations where not needed

Clean up some intent statements

[apcraig]

I think I've reviewed all the current optional arguments in Icepack now and checked implementation. There are probably other Icepack arguments that could be made optional, but we'll need to come up with some suggestions if we want to do that.

I will merge this to the E3SM Icepack branch after it's merged and update CICE as well.

[apcraig]

I think I've updated the changes requested. I retested full test suite on cheyenne with Icepack and CICE, everything passes and is bit-for-bit. This is ready for another review/merge.