[CMake] Retire Polly's FindCUDA.cmake in favour of CMake's default FindCUDA.cmake script.

Patch by: Singapuram Sanjay

Reviewers: grosser, philip.pfaffe

Reviewed By: philip.pfaffe

Subscribers: pollydev, mgorny

Tags: #polly

Differential Revision: https://reviews.llvm.org/D33669

llvm-svn: 304818