Remove codegen caching

[ponyisi]

Codegen caching on the client side is not saving very much network activity but potentially causes users to be surprised that backend installations apparently don't support transformations that they should. In any case we obtain this data on every session because we request the capabilities, so we can actually eliminate the caching with zero added cost to the backend.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.49%. Comparing base (188c034) to head (43a0666).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #619      +/-   ##
==========================================
- Coverage   96.50%   96.49%   -0.01%     
==========================================
  Files          29       29              
  Lines        1974     1942      -32     
==========================================
- Hits         1905     1874      -31     
+ Misses         69       68       -1     

Flag	Coverage Δ
unittests	96.49% <100.00%> (-0.01%)	⬇️

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[BenGalewsky]

Just wonder about keeping that backend parameter in the servicex client method, but otherwise this is a better approach. Thanks