style: include `UC_USELESS_OBJECT`

[vil02]

This PR includes the UC_USELESS_OBJECT SpotBugs rule. The removed App class was redundant.

Related to #5122.

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized it.
• [x] All filenames are in PascalCase.
• [x] All functions and variable names follow Java naming conventions.
• [x] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• [x] All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 37.36%. Comparing base (2513ccd) to head (01671cb). Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5127      +/-   ##
============================================
+ Coverage     37.34%   37.36%   +0.02%     
  Complexity     2350     2350              
============================================
  Files           517      517              
  Lines         15622    15618       -4     
  Branches       2971     2971              
============================================
+ Hits           5834     5836       +2     
+ Misses         9500     9495       -5     
+ Partials        288      287       -1     

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