Remove hlint as default HaskellTool

Hlint is usually used once in a pipeline, not per-job
or per architecture/platform. Thus, we only need one
hlint image.

It can easily be installed in an x86_64 image:
  curl -sSL https://raw.github.com/ndmitchell/hlint/master/misc/run.sh | sh -s .

This might also fix image build issues.
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