[tfjs-backend-nodegl] Remove hard-coded WebGL flags

[nkreeger]

Currently, the tfjs-backend-nodegl env startup script hard-codes WebGL global flags. This task should remove those flags and let the environment automatically pick these features up.

[google-ml-butler]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you.

[google-ml-butler]

Closing as stale. Please @mention us if this needs more attention.