fix: Generalize a couple remaining Proctortrack references

[kdmccormick]

Description & Supporting info

Just a few leftovers from: #2645

See openedx/openedx-platform#36329 for full context. Basically: The platform no longer assumes that Proctortrack exists. Instead, it just has an idea that some proctoring providers require an escalation email, which operators can configure on a per-provider basis.

Testing instructions

Ensure ENABLE_PROCTORED_EXAMS is true site-wide.

Configure a PROCTORING_BACKEND with option requires_escalation_email: true. Ensure the backend is installed.

In a studio course, go to Pages and Resources -> Proctored Exam Settings. Select the provider you just configured.

Observe these new strings in the UI.

Best Practices Checklist

We're trying to move away from some deprecated patterns in this codebase. Please
check if your PR meets these recommendations before asking for a review:

(I confirmed that none of these apply)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.89%. Comparing base (833a838) to head (c576e53).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #2746    +/-   ##
========================================
  Coverage   94.89%   94.89%            
========================================
  Files        1235     1235            
  Lines       28254    28254            
  Branches     6222     6408   +186     
========================================
  Hits        26813    26813            
+ Misses       1383     1370    -13     
- Partials       58       71    +13     

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