Fix/remove defunct untested code

[hredestig]

fixes #383 #384

[codecov-io]

Codecov Report

Merging #400 into devel-2 will increase coverage by 1.49%.
The diff coverage is 56.66%.

@@             Coverage Diff             @@
##           devel-2     #400      +/-   ##
===========================================
+ Coverage    64.05%   65.54%   +1.49%     
===========================================
  Files           67       65       -2     
  Lines         8098     7770     -328     
  Branches      1406     1351      -55     
===========================================
- Hits          5187     5093      -94     
+ Misses        2656     2434     -222     
+ Partials       255      243      -12

Impacted Files	Coverage Δ
cobra/test/test_flux_analysis.py	87.44% <ø> (+2.34%)	✅
cobra/util/init.py	100% <ø> (ø)	✅
cobra/topology/reporter_metabolites.py	0% <ø> (ø)	✅
cobra/test/test_manipulation.py	100% <100%> (+10.76%)	✅
cobra/exceptions.py	63.63% <20%> (-36.37%)	❌
cobra/design/design_algorithms.py	50% <50%> (+29.84%)	✅
cobra/flux_analysis/gapfilling.py	50% <50%> (-4.95%)	❌
cobra/core/solution.py	83.33% <ø> (-2.09%)	❌
cobra/core/Reaction.py	83.98% <ø> (-0.44%)	❌
... and 1 more

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[cdiener]

Makes sense :)

[pstjohn]

Awesome, looks nice

[pstjohn]

Would you want to also include those __add__ methods we talked about removing? In model.py, for instance.

[hredestig]

I'd prefer to see them moved out from the Model class I think but fits just as well in a different PR