Memory usage fixes

- Refactor `ifaceDeclMap` to drastically reduce memory footprint. We
  no longer store all declarations associated with a given name, since
  we only cared to determine if the only declaration associated with a
  name was a value declaration. Change the `DeclMap` type to better
  reflect this.
- Drop pre-renaming export items after the renaming step. Since the
  Hoogle backend used the pre-renamed export items, this isn't trivial.
  We now generate Hoogle output for exported declarations during the
  renaming step (if Hoogle output /should/ be generated), and store that
  with the renamed export item.
- Slightly refactor Hoogle backend to handle the above change and allow
  for early generation of Hoogle output.
- Remove the `ifaceRnDocMap` and `ifaceRnArgMap` fields of the
  `Interface` type, as they were never used.
- Remove some unnecessary strictness
- Remove a lot of dead code from `Syb` module