[cuda] NFC: rename cuda2 to cuda

This is the last step of refreshing the cuda HAL implementation. Mostly done via the following command: ```sh find runtime/ -type f -exec sed -i 's/CUDA2/CUDA/g' {} \; find runtime/ -type f -exec sed -i 's/cuda2/cuda/g' {} \; ``` Related to https://github.com/openxla/iree/issues/13245