remove CUDA_VISIBLE_DEVICES

[mselensky]

• Following some discussion with Haley and Olivia, removing CUDA_VISIBLE_DEVICES to avoid confusion as it is generally unnecessary with Slurm. SLURM_JOB_GPUS will reflect the real GPU device IDs in a given job if are multiple users running jobs on one node, so that variable should be preferred anyway.
• Also minor typo fix in my example Numba code