[BE] Delete BUILD_SPLIT_CUDA option (#87502)
As we are linking with cuDNN and cuBLAS dynamically for all configs anyway, as statically linked cuDNN is different library than dynamically linked one, increases default memory footprint, etc, and libtorch_cuda even if compiled for all GPU architectures is no longer approaching 2Gb binary size limit, so BUILD_SPLIT_CUDA can go away.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87502
Approved by: https://github.com/atalman
