Clean up JUnit3 references

[jibidus]

JUnit3 is not supported.

(related to #2569)

[codecov-commenter]

Codecov Report

Merging #2570 (7b6de8b) into main (02d6356) will decrease coverage by 0.10%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main    #2570      +/-   ##
============================================
- Coverage     86.75%   86.65%   -0.11%     
+ Complexity     2796     2795       -1     
============================================
  Files           321      321              
  Lines          8368     8368              
  Branches       1024     1024              
============================================
- Hits           7260     7251       -9     
- Misses          840      849       +9     
  Partials        268      268              

Impacted Files	Coverage Δ
src/main/java/org/mockito/MockitoAnnotations.java	45.45% <ø> (ø)
...a/org/mockito/internal/junit/ExceptionFactory.java	75.00% <ø> (-25.00%)	⬇️
...ions/verification/junit/ArgumentsAreDifferent.java	0.00% <0.00%> (-66.67%)	⬇️

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[TimvdLippe]

Thanks for the quick PR!