Remove aiodocker and related fixtures, since they are not used anyway.

[jettify]

What do these changes do?

Are there changes in behavior for the user?

Related issue number

Checklist

• [ ] I think the code is well written
• [ ] Unit tests for the changes exist
• [ ] Documentation reflects the changes
• [ ] Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
  • ensure type is one of the following:
  • .feature: Signifying a new feature.
  • .bugfix: Signifying a bug fix.
  • .doc: Signifying a documentation improvement.
  • .removal: Signifying a deprecation or removal of public API.
  • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: Fix issue with non-ascii contents in doctest text files.

[codecov[bot]]

Codecov Report

Merging #455 (d42bba6) into master (9711e9c) will not change coverage. Report is 1 commits behind head on master. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #455   +/-   ##
=======================================
  Coverage   87.01%   87.01%           
=======================================
  Files           6        6           
  Lines         493      493           
  Branches       73       73           
=======================================
  Hits          429      429           
  Misses         48       48           
  Partials       16       16           

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