HIR cleanup: Unify generic param bounds and where clause

[jdupak]

This is syntax sugar with no difference in meaning. No need to have tham split in two places.

@philberty agree?

[CohenArthur]

sounds like a good idea to me

[philberty]

Yes this makes me happy @jdupak go for it. I left them because I was not sure if there was special handling here