[CUDA] Removed unused __nvvm_* builtins with non-generic pointers.

They were hot even hooked into CGBuiltin's machinery. Even if they were,
CUDA does not support AS-specific pointers, so there would be no legal way
no way to call these builtins.

This came up in D47154.

Differential Revision: https://reviews.llvm.org/D47845

llvm-svn: 335168