Drop busybox /bin/sh symlinks, move off -dev distroless tag

[rajathagasthya]

Part of NVIDIA/cloud-native-team#299.

The nvidia-container-toolkit runtime container's Dockerfile uses the
same pattern as several other NVIDIA cloud-native repos: a -dev
distroless base plus an explicit /bin/sh busybox symlink — and it
does this in two build stages. NVIDIA STIG policy is dropping
-dev distroless variants as approved parent images, so this needs
to be replaced.

Scope: deployments/container/Dockerfile

• Line 58: FROM nvcr.io/nvidia/distroless/go:v4.0.2-dev AS packaging → drop -dev
• Lines 61-62: drop SHELL ["/busybox/sh", "-c"] and RUN ln -s /busybox/sh /bin/sh
• Line 147: FROM nvcr.io/nvidia/distroless/go:v4.0.2-dev AS application → drop -dev
• Lines 150-151: drop SHELL and ln -s symlink

The runtime ENTRYPOINT (/work/nvidia-ctk-installer, line 175) is
already a Go binary and doesn't need a shell. No Kubernetes manifests
in the repo use sh -c. Mechanical change.

Acceptance:

• Both stages no longer reference -dev distroless tags
• No SHELL directives or /bin/sh symlinks remain
• Image build succeeds and the runtime works correctly when
  consumed by gpu-operator