Remove and metrics-aggregation tests

[uhafner]

Remove autograding and metrics-aggregation tests as these plugins is not supported anymore. Let's see if I find some spare time to bring those plugins up-to-date again later.

[codecov]

Codecov Report

Merging #1472 (3e4389c) into master (4ca600a) will increase coverage by 1.28%.
The diff coverage is 71.42%.

@@             Coverage Diff              @@
##             master    #1472      +/-   ##
============================================
+ Coverage     80.53%   81.82%   +1.28%     
+ Complexity     1475     1407      -68     
============================================
  Files           254      245       -9     
  Lines          5647     5332     -315     
  Branches        426      397      -29     
============================================
- Hits           4548     4363     -185     
+ Misses          947      850      -97     
+ Partials        152      119      -33     

Impacted Files	Coverage Δ
...kins/plugins/analysis/core/model/ResultAction.java	60.78% <ø> (+1.16%)	⬆️
...s/plugins/analysis/core/steps/AnnotatedReport.java	100.00% <ø> (ø)
.../plugins/analysis/core/steps/IssuesAggregator.java	100.00% <ø> (ø)
...ns/plugins/analysis/core/util/ModelValidation.java	91.66% <ø> (+20.88%)	⬆️
...enkins/plugins/analysis/core/util/QualityGate.java	76.11% <ø> (+25.63%)	⬆️
...lugins/analysis/warnings/axivion/AxivionSuite.java	29.92% <ø> (+3.14%)	⬆️
.../analysis/warnings/groovy/ParserConfiguration.java	62.79% <0.00%> (ø)
...ns/analysis/core/steps/AnalysisStepDescriptor.java	22.85% <20.00%> (+2.26%)	⬆️
...ins/plugins/analysis/warnings/tasks/OpenTasks.java	39.74% <28.57%> (-0.52%)	⬇️
...ns/plugins/analysis/core/steps/IssuesRecorder.java	72.39% <66.66%> (+4.38%)	⬆️
... and 15 more

... and 1 file with indirect coverage changes

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