Clean up `docs/make.jl`

[abelsiqueira]

Copied from #355

For docs:

• The nice_name is not needed because Documenter.jl will automatically pull the title of the markdown file (and not the file name) if you put file names instead of pairs in the pages argument to makedocs
• Remove doctest=true because it is the default
• Remove linkcheck=false because Documenter.jl's linkcheck also checks internal references
• Remove repo=... because Documenter.jl figures it out itself from a GitHub repo
• Remove prettyurls=true because it is the default
• Remove assets=... to have default styling
• Don't activate push_preview, or add a CI workflow to clean up the previews after closing

[abelsiqueira]

repo only works after the GitHub repo is set. For new packages (and for testing the package) it is better to leave it.

[abelsiqueira]

Leaving the push_preview in favour of having #63