Cleanup Dockerfile's

[rawkode]

This commit tries to remove as many redundant layers as possible, while
still maintaining readability.

[rawkode]

I reckon I can consolidate these Dockerfile's into a single one, using multi-stage builds; but this will require additional pull requests.

[codecov]

Codecov Report

Merging #711 into v4 will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##               v4     #711   +/-   ##
=======================================
  Coverage   84.35%   84.35%           
=======================================
  Files          36       36           
  Lines         965      965           
  Branches      107      107           
=======================================
  Hits          814      814           
  Misses         93       93           
  Partials       58       58

---

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[thinkingserious]

Hello @rawkode,

Thanks again for the PR!

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[thinkingserious]

Hello @rawkode,

Thanks again for the PR!

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