Remove admin select2 custom css

[int-y1]

remove width: 100% on select2 elements. this fixes the styling for the "Organizations" field. see screenshot:

i tested all fields except interface.py SolutionForm (is SolutionForm used anywhere?)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 47.73%. Comparing base (fd7fb05) to head (9b82903).
Report is 63 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2400      +/-   ##
==========================================
+ Coverage   46.76%   47.73%   +0.96%     
==========================================
  Files         251      259       +8     
  Lines       13317    13706     +389     
==========================================
+ Hits         6228     6542     +314     
- Misses       7089     7164      +75     

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