Clean up remaining bits of the install rule (#660)

Authored by snowleopard on Aug 27 2018, 6:26 AM.

Description

Clean up remaining bits of the install rule (Trac #660)

Trac #531 removed install rules (src/Rules/Install.hs), but left a lot of supporting code that is now unused.

Hopefully, this clean up completes the removal of install rules. If they are ever coming back to Hadrian in any shape, some useful code can be recovered here.

See Trac #540.