Remove unnecessary free-variables from renamer

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.