simplify imports Omegaconf

[Borda]

What does this PR do?

Partial #4859

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Did you have fun?

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[codecov]

Codecov Report

Merging #4873 (eaa60ae) into master (442d57f) will decrease coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #4873   +/-   ##
======================================
- Coverage      93%     93%   -0%     
======================================
  Files         118     118           
  Lines        9004    8991   -13     
======================================
- Hits         8383    8370   -13     
  Misses        621     621           

[tchaton]

LTGM !