Remove some warnings

[ewu63]

Purpose

Two types of warnings are removed:

• warning on failing to import mpi4py, IMO this is a bit annoying for those that are not using the parallel features
• deprecation warnings for things that were removed 2+ years ago

We may want to make a release after this is merged, and clearly explain in the release notes that these deprecations are now removed.

Expected time until merged

Not urgent

Type of change

• 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

Checklist

• I have run flake8 and black to make sure the Python code adheres to PEP-8 and is consistently formatted
• I have formatted the Fortran code with fprettify or C/C++ code with clang-format as applicable
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation

[codecov]

Codecov Report

Merging #343 (048a462) into main (33cca24) will decrease coverage by 11.43%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             main     #343       +/-   ##
===========================================
- Coverage   83.86%   72.43%   -11.43%     
===========================================
  Files          22       22               
  Lines        3365     3352       -13     
===========================================
- Hits         2822     2428      -394     
- Misses        543      924      +381     

Impacted Files	Coverage Δ
pyoptsparse/pyOpt_MPI.py	70.96% <ø> (+3.32%)	⬆️
pyoptsparse/pyOpt_optimization.py	78.71% <ø> (-0.29%)	⬇️
pyoptsparse/__init__.py	100.00% <100.00%> (ø)

... and 7 files with indirect coverage changes

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[marcomangano]

LGTM, can you bump the minor version? We are finally introducing some backward incompatibility so I think it's appropriate.

You will also have to merge this yourself as the issue with RTD is still unsolved

[ewu63]

I can bump the version here, but I'd like #341 merged first in that case. Maybe @eirikurj can do it, otherwise I can do it too but it feels weird to use admin powers to merge my own PR.