repro: remove on_unchanged kwarg and _repro_callback

[skshetry]

No description provided.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.02 ⚠️

Comparison is base (6e6d925) 90.64% compared to head (154aa6d) 90.63%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9674      +/-   ##
==========================================
- Coverage   90.64%   90.63%   -0.02%     
==========================================
  Files         472      472              
  Lines       36289    36280       -9     
  Branches     5221     5218       -3     
==========================================
- Hits        32895    32882      -13     
- Misses       2810     2812       +2     
- Partials      584      586       +2     

Impacted Files	Coverage Δ
dvc/repo/experiments/executor/base.py	80.05% <100.00%> (-0.26%)	⬇️
dvc/repo/reproduce.py	96.26% <100.00%> (+0.76%)	⬆️

... and 1 file with indirect coverage changes

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