Tidy up and dry up code

[primer]

Tidy up and dry up code

[emplums]

@broccolini I started working on replacing some of the extended Link components with plain Link components since we've now got typography system props in primer/components and a few other Link bugs worked out... one thing I ran into was not being able to access all of our typography theme values (such as mono from fonts, to be used with the styled-system fontFamily props).

What do you think about using the primer/components theme in primer.style instead of what we've got in primer.style now (a few imports from primitives + the default theme values from styled system)? I think it makes sense to build this site with the theme we're shipping with primer/components but not sure if there's any reason in particular that you stuck with imports from primitives? The only hitch I'm seeing is that we'll need to rework a bunch of the spacing since the default breakpoints + spacing values from styled-system are pretty different from our values shipped with primer/components. Let me know what you think!

[broccolini]

This is now outdated.