Remove FindCUDA from source tarball
When we decided to bundle FindCUDA.cmake and supporting files to keep
our developer and Jenkins builds free of warnings, we did not take
care to ensure that the user gets the behaviour from their cmake,
since the combination of their cmake and its FindCUDA.cmake is much
more likely to work correctly than their cmake and FindCUDA.cmake from
cmake 3.4.3.
The testing of the release tarball as part of the release workflow
will ensure that we don't silently ship a broken CUDA build.
Refs #2276
Change-Id: I9ed6fa97921eb5c3ce3b4a6ecc401b4dd26e1251