Improve code cleaning

[michael-doubez]

Clean pom and update checkstyle

Testing done

Submitter checklist

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1. Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
2. Ensure that the pull request title represents the desired changelog entry
3. Please describe what you did
4. Link to relevant issues in GitHub or Jira
5. Link to relevant pull requests, esp. upstream and downstream changes
6. Ensure you have provided tests - that demonstrates feature works or fixes the issue

[codecov]

Codecov Report

Attention: Patch coverage is 58.26772% with 53 lines in your changes are missing coverage. Please review.

Project coverage is 73.16%. Comparing base (22331f0) to head (c3d9244).
Report is 9 commits behind head on master.

Files	Patch %	Lines
...va/org/jenkinsci/plugins/oic/OicSecurityRealm.java	53.06%	34 Missing and 12 partials ⚠️
...ain/java/org/jenkinsci/plugins/oic/OicSession.java	57.14%	2 Missing and 1 partial ⚠️
...gins/oic/WellKnownOpenIDConfigurationResponse.java	60.00%	2 Missing ⚠️
...sci/plugins/oic/JenkinsAwareConnectionFactory.java	0.00%	0 Missing and 1 partial ⚠️
...va/org/jenkinsci/plugins/oic/OicTokenResponse.java	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #289      +/-   ##
============================================
+ Coverage     71.90%   73.16%   +1.25%     
+ Complexity      194      189       -5     
============================================
  Files             9        9              
  Lines           744      775      +31     
  Branches        124      113      -11     
============================================
+ Hits            535      567      +32     
- Misses          150      151       +1     
+ Partials         59       57       -2     

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