fix(mf6): omit removed fields from generated code

[wpbonelli]

Filter out fields marked in DFNs as removed from the generated classes in the MF6 module. Before, removed fields were included in the generated classes and would be written to input files, which would cause MF6 to raise an error.

And remove usages of options recently been removed from MF6.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.6%. Comparing base (556c088) to head (f185c29).
⚠️ Report is 197 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/mf6/utils/codegen/__init__.py	0.0%	2 Missing ⚠️
flopy/mf6/mfmodel.py	0.0%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2804      +/-   ##
===========================================
+ Coverage     55.5%    71.6%   +16.0%     
===========================================
  Files          644      661      +17     
  Lines       124135   132990    +8855     
===========================================
+ Hits         68947    95243   +26296     
+ Misses       55188    37747   -17441     

Files with missing lines	Coverage Δ
flopy/mf6/utils/codegen/filters.py	0.0% <ø> (ø)
flopy/mf6/mfmodel.py	57.3% <0.0%> (-23.6%)	⬇️
flopy/mf6/utils/codegen/__init__.py	0.0% <0.0%> (ø)

... and 580 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.