Remove galaxy tool util dependency

[Midnighter]

As suggested by @fabianegli in the discussion on Slack, this PR copies the relevant code into the mulled module. However, there are two caveats:

1. Copying code like this is nasty since we burden ourselves with ensuring its correctness and maintenance. We will also have to watch for upstream changes. However, I expect that this code is extremely stable since any change would break thousands of existing mulled images. So I think it is safe to make an exception here.
2. And this may be a killer for these changes: The original source code is released under an Academic Free License version 3.0; I have no idea if that is compatible with the MIT License. I suspect that might rather not be the case.

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated

[codecov]

Codecov Report

Merging #2195 (3affb8a) into dev (7f30502) will decrease coverage by 0.15%.
The diff coverage is 66.10%.

@@            Coverage Diff             @@
##              dev    #2195      +/-   ##
==========================================
- Coverage   71.57%   71.43%   -0.15%     
==========================================
  Files          77       77              
  Lines        8369     8415      +46     
==========================================
+ Hits         5990     6011      +21     
- Misses       2379     2404      +25     

Impacted Files	Coverage Δ
nf_core/modules/mulled.py	68.88% <66.10%> (-8.89%)	⬇️
nf_core/modules/test_yml_builder.py	50.66% <0.00%> (-1.34%)	⬇️
nf_core/modules/lint/module_patch.py	58.10% <0.00%> (-0.56%)	⬇️
nf_core/sync.py	74.68% <0.00%> (-0.43%)	⬇️
nf_core/components/list.py	68.42% <0.00%> (-0.42%)	⬇️
nf_core/create.py	64.63% <0.00%> (-0.39%)	⬇️
nf_core/utils.py	82.13% <0.00%> (-0.25%)	⬇️
nf_core/components/create.py	79.43% <0.00%> (-0.10%)	⬇️
nf_core/modules/modules_json.py	80.34% <0.00%> (+0.07%)	⬆️

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[fabianegli]

In my understanding of what I wrote, I never actually proposed plain copy pasting of the code that is now in this PR and I think this is not warranted.

As for the licensing issue: It would be great to have some input from the maintainers of the original repo if this copy/pasting would be regarded as fair use - and I am not sure how this copied code would need to be marked for copyright purposes and if it would have to propagate to the top level of the repository.

Personally, I think this PR in the current state is creating more and more difficult questions than it answers.

[Midnighter]

Closing this one. Superseded by #2199.