Remove unused cobertura plugin

[tcnghia]

Description

Remove unused Cobertura plugin.

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #[issue number]

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

Merging #346 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #346   +/-   ##
=========================================
  Coverage     75.71%   75.71%           
  Complexity      709      709           
=========================================
  Files            69       69           
  Lines          2359     2359           
  Branches        244      244           
=========================================
  Hits           1786     1786           
  Misses          418      418           
  Partials        155      155           

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