style: do not suppress serial

[vil02]

This PR includes serial into the active compiler warnings.

The BackEdgeException did not provide any additional useful information to the user, so I decided to remove it.

Continuation of #5165.

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• 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 ✅

Project coverage is 38.57%. Comparing base (5ee98ee) to head (87052f1).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #5168   +/-   ##
=========================================
  Coverage     38.57%   38.57%           
- Complexity     2378     2379    +1     
=========================================
  Files           516      516           
  Lines         15315    15313    -2     
  Branches       2957     2957           
=========================================
  Hits           5907     5907           
+ Misses         9122     9121    -1     
+ Partials        286      285    -1     

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[BamaCharanChhandogi]

Thanks.