Deprecate zsalinity

[apcraig]

PR checklist

• Short (1 sentence) summary of your PR:
  Deprecate zsalinity
• Developer(s):
  apcraig
• Suggest PR reviewers from list in the column to the right.
• Please copy the PR test results link or provide a summary of testing completed below.
  Results are bit for bit and as expected, https://github.com/CICE-Consortium/Test-Results/wiki/cice_by_hash_forks#e392863dde37235778528485a562229e254cefea
• How much do the PR code changes differ from the unmodified code?
  • bit for bit
  • different at roundoff level
  • more substantial
• Does this PR create or have dependencies on Icepack or any other models?
  • Yes, requires update to Icepack
  • No
• Does this PR update the Icepack submodule? If so, the Icepack submodule must point to a hash on Icepack's main branch.
  • Yes
  • No
• Does this PR add any new test cases?
  • Yes
  • 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/. A test build of the technical docs will be performed as part of the PR testing.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please document the changes in detail, including why the changes are made. This will become part of the PR commit log.

Remove zsalinity code (was deprecated via abort previously)

• Remove zsalinity variables restart_zsal, solve_zsal, fzsal, grid_oS, l_skS,

• Update Icepack interface calls

• Remove fzsal from coupling_prep subroutine and interface

• Support zsalinity namelist for backwards compatibility. Has no effect except if solve_zsal or restart_zsal = true then the code aborts.

• Update documentation

• Update Icepack to #5feadd007a58f

[apcraig]

Will require an update to Icepack still to be done.

One question from me. I have left the ability to read old namelist with zsalinity variables in it. They are ignored except if solve_zsal is set to true in which case the code aborts. Those namelist variables are removed from the default icepack_in and are not documented anymore. Should we formally remove support for reading those namelist as well? That would mean an older namelist input file would fail if used with this version.

[apcraig]

Have run full test suites with Icepack and CICE, all results look good and are bit-for-bit. https://github.com/CICE-Consortium/Test-Results/wiki/cice_by_hash_forks#e392863dde37235778528485a562229e254cefea.