clean: Remove dead code [ TECH-1618 ]

[lucaCambi77]

https://dhis2.atlassian.net/browse/TECH-1618

There isn't much dead code left in the tracker to clean up actually.
With this PR, we do some quick cleanup based on IntelliJ code inspection

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

0.0% Coverage
0.0% Duplication

[codecov]

Codecov Report

Merging #15784 (423a0e7) into master (e434a0b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #15784   +/-   ##
=========================================
  Coverage     66.28%   66.28%           
- Complexity    31415    31416    +1     
=========================================
  Files          3492     3492           
  Lines        130200   130199    -1     
  Branches      15211    15211           
=========================================
+ Hits          86306    86307    +1     
+ Misses        36801    36800    -1     
+ Partials       7093     7092    -1     

Flag	Coverage Δ
integration	50.01% <100.00%> (+<0.01%)	⬆️
integration-h2	32.35% <66.66%> (+<0.01%)	⬆️
unit	30.31% <100.00%> (-0.01%)	⬇️

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

Files	Coverage Δ
...er/export/enrollment/DefaultEnrollmentService.java	64.66% <ø> (ø)
...r/export/enrollment/EnrollmentOperationParams.java	75.00% <ø> (ø)
...his/tracker/export/event/EventOperationParams.java	80.00% <ø> (ø)
...port/relationship/RelationshipOperationParams.java	66.66% <ø> (ø)
...rt/trackedentity/TrackedEntityOperationParams.java	80.00% <ø> (ø)
...rackedentity/aggregates/mapper/AbstractMapper.java	100.00% <ø> (ø)
.../dhis/tracker/imports/TrackerBundleReportMode.java	100.00% <100.00%> (ø)
...p/dhis/tracker/imports/preheat/TrackerPreheat.java	89.08% <100.00%> (ø)
...sp/dhis/tracker/imports/programrule/IssueType.java	100.00% <100.00%> (ø)
.../imports/validation/validator/ValidationUtils.java	91.54% <ø> (-0.12%)	⬇️

... and 1 file with indirect coverage changes

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