remove legacy CUDA non-bonded kernels

This commit drops the legacy set of kernels which were optimized for use
with CUDA compilers 3.2 and 4.0 (previous to the switch to llvm backend
in 4.1).

For now the only consequence is slight performance degradation with CUDA
3.2/4.0, the build system still requires CUDA >=3.2 as the kernels do
build with the older CUDA compilers. Whether to require at least CUDA
4.1 will be decided later.

Refs #1382

Change-Id: I75d31b449e5b5e10f823408e23f35b9a7ac68bae