Default to static linking of libcudart

[bdice]

Summary

• Enable static linking of libcudart by default (CUDA_STATIC_RUNTIME=ON)
• Remove cuda-cudart from conda recipe run requirements (no longer needed when statically linked)

This is part of a RAPIDS-wide effort to switch to static CUDA runtime linking. See https://github.com/rapidsai/build-planning/issues/235 for tracking.

Changes

• cpp/CMakeLists.txt: Change CUDA_STATIC_RUNTIME default from OFF to ON
• conda/recipes/cuml/recipe.yaml: Remove cuda-cudart from run deps
• conda/recipes/libcuml/recipe.yaml: Remove cuda-cudart from run deps (2 outputs)

Note: Python builds already use CUDA_STATIC_RUNTIME=ON (set in python/libcuml/CMakeLists.txt).