Implement removals indicated by deprecations in Cantera 3.0

[speth]

Changes proposed in this pull request

• Bump version to 3.1.0a1
• Remove code slated for removal and changes noted as occurring "after Cantera 3.0"
• Make relevant simplifications enabled by removal of deprecated code
• Remove some unused test data files

I tried to break up the "interesting" changes into separate commits. This might be easiest to review on a commit-by-commit basis, where the commits "Remove code deprecated in Cantera 3.0" and "Remove deprecated Python code" consist almost entirely of straight removals of deprecated code.

Checklist

• [x] The pull request includes a clear description of this code change
• [x] Commit messages have short titles and reference relevant issues
• [x] Build passes (scons build & scons test) and unit tests address code coverage
• [x] Style & formatting of contributed code follows contributing guidelines
• [x] The pull request is ready for review

[codecov[bot]]

Codecov Report

Merging #1605 (fcab50a) into main (806842d) will increase coverage by 2.07%. The diff coverage is 71.07%.

@@            Coverage Diff             @@
##             main    #1605      +/-   ##
==========================================
+ Coverage   70.59%   72.66%   +2.07%     
==========================================
  Files         379      370       -9     
  Lines       59185    56259    -2926     
  Branches    21270    20353     -917     
==========================================
- Hits        41781    40882     -899     
+ Misses      14325    12374    -1951     
+ Partials     3079     3003      -76     

Files Changed	Coverage Δ
include/cantera/base/Array.h	96.00% <ø> (ø)
include/cantera/kinetics/BulkKinetics.h	100.00% <ø> (+50.00%)	:arrow_up:
include/cantera/kinetics/ChebyshevRate.h	100.00% <ø> (ø)
include/cantera/kinetics/Falloff.h	93.02% <ø> (+11.39%)	:arrow_up:
include/cantera/kinetics/ImplicitSurfChem.h	100.00% <ø> (ø)
include/cantera/kinetics/InterfaceKinetics.h	87.50% <ø> (ø)
include/cantera/kinetics/InterfaceRate.h	87.87% <ø> (ø)
include/cantera/kinetics/Kinetics.h	32.43% <ø> (-0.24%)	:arrow_down:
include/cantera/kinetics/PlogRate.h	100.00% <ø> (ø)
include/cantera/kinetics/Reaction.h	90.00% <ø> (+5.00%)	:arrow_up:
... and 115 more

... and 7 files with indirect coverage changes

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