fix(eslint-plugin): [no-unused-vars] false-positive with class expressions

[bradzacher]

Fixes #2831

[typescript-eslint]

Thanks for the PR, @bradzacher!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[codecov]

Codecov Report

Merging #2833 (ecb1a61) into master (af9ab87) will increase coverage by 0.00%.
The diff coverage is 85.71%.

@@           Coverage Diff           @@
##           master    #2833   +/-   ##
=======================================
  Coverage   92.72%   92.73%           
=======================================
  Files         309      309           
  Lines       10330    10332    +2     
  Branches     2926     2926           
=======================================
+ Hits         9579     9581    +2     
  Misses        347      347           
  Partials      404      404           

Flag	Coverage Δ
unittest	92.73% <85.71%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...s/eslint-plugin/src/util/collectUnusedVariables.ts	91.17% <85.71%> (+0.07%)	⬆️