Base image has been relicensed

The base image for this container is `nvidia/opengl:1.2-glvnd-runtime-ubuntu20.04`.
https://github.com/google/android-emulator-container-scripts/blob/94592e7dbb46d28ec46497c0bdd00c3a95afe1cc/emu/templates/Dockerfile.system_image#L22

NVIDIA relicensed this container image and imposed its own restrictive non-OSS license.
https://gitlab.com/nvidia/container-images/opengl/-/commit/bb8e78b231c77921fdd7c65d88c4febd28a8adc6#

As a result, Android image files generated by emu_docker may have the following restrictions:.
* Underage users are restricted from using this image
* Use on machines without an NVIDIA GPU is restricted (Even if the `--gpu` flag is not specified in emu_docker)

The current Android image is based on the old-licensed base image, so it does not have these restrictions, but licensing issues will arise the next time Google updates the system_image, or when users rebuild the image themselves.