[NVPTX] Remove NVPTXFavorNonGenericAddrSpaces pass.

Summary:
This has been replaced by the NVPTXInferAddressSpaces pass.  We've had
the new one as the default with the old one accessible via a flag for
some months now, and we've had no problems.

Reviewers: tra

Subscribers: llvm-commits, jholewinski, jingyue, mgorny

Differential Revision: https://reviews.llvm.org/D26165

llvm-svn: 285642