nongnu: game-client: Merge NVIDIA and non-NVIDIA containers.
* nongnu/packages/game-client.scm (steam-container-for,steam-for)
(heroic-container-for,heroic-for): New procedures.
(steam-container,steam-nvidia-container): Deprecated by steam-container-for.
(steam,steam-nvidia): Define with steam-for.
(heroic-container,heroic-nvidia-container): Deprecated by heroic-container-for.
(heroic,heroic-nvidia): Define with heroic-for.
(steam-nvidia-container-libs,steam-ld.so.conf,steam-ld.so.cache)
(steam-nvidia-ld.so.conf,steam-nvidia-ld.so.cache): Delete variables.
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