Remove unnecessary free-variables from renamer
The renamer used to be responsible for making sure that all interfaces with instance decls (other than orphans) were loaded. But TH makes that impossible, so the typechecker does it, via checkWiredInTyCon. This patch simply removes redundant additions to the free-variable set in the renamer, which were there, I believe, solely to ensure that the instances came in. Removing them should change nothing, but it's a useful clean up.