[v5.0.1] Remove SigmaProp.isProven method

[aslesarenko]

This PR depends on #543 which is necessary to fix the tests (actually rewrite some scripts)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 71.23%. Comparing base (680e5be) to head (703470a). Report is 196 commits behind head on v5.0.4-RC.

:exclamation: Current head 703470a differs from pull request most recent head 9a004b0. Consider uploading reports for the commit 9a004b0 to get more accurate results

Additional details and impacted files

@@              Coverage Diff              @@
##           v5.0.4-RC     #800      +/-   ##
=============================================
- Coverage      71.38%   71.23%   -0.15%     
=============================================
  Files            246      248       +2     
  Lines          18683    18781      +98     
  Branches         597      627      +30     
=============================================
+ Hits           13336    13379      +43     
- Misses          5347     5402      +55     

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