Clean up i18n in __str__

[int-y1]

This affects the following admin pages:

Home › Online Judge › Classes › Foo Class in DMOJ: Modern Online Judge
Home › Online Judge › Comments › b:1 by admin
Home › Online Judge › Contest participations › d in Fake Contest 111
Home › Online Judge › Submissions › Submission 12 of testpdf2 by admin

SubmissionSource.__str__ was tested by visiting a submission.

WebAuthnCredential.__str__ was tested by visiting a user profile.

[codecov-commenter]

Codecov Report

Merging #1932 (0b906c2) into master (8b29591) will not change coverage.
The diff coverage is 33.33%.

@@           Coverage Diff           @@
##           master    #1932   +/-   ##
=======================================
  Coverage   46.41%   46.41%           
=======================================
  Files         235      235           
  Lines       13107    13107           
=======================================
  Hits         6084     6084           
  Misses       7023     7023           

Impacted Files	Coverage Δ
judge/models/comment.py	39.61% <0.00%> (ø)
judge/models/profile.py	81.97% <0.00%> (ø)
judge/models/contest.py	96.20% <25.00%> (ø)
judge/models/submission.py	90.50% <100.00%> (ø)

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[quantum5]

Otherwise LGTM. Note that __str__ is really only used in the admin.

[Ninjaclasher]

LGTM