Simplify ccache instructions in CONTRIBUTING.md (#62549)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62549
When building CUDA files with native CMake support, it will respect the
`CMAKE_CUDA_COMPILER_LAUNCHER` setting. So, there's no need for symlinks.
Test Plan: Imported from OSS
Reviewed By: bdhirsh
Differential Revision: D30498488
Pulled By: malfet
fbshipit-source-id: 71c2ae9d4570cfac2a64d777bc95cda3764332a0
