[Newton] Drop the unused lockfile input from the kit-less build

[hujc7]

1. Summary

• Stops copying uv.lock into the kit-less build context, and stops gating the kit-less CI job on it.
• Two files, +1 / -2.

2. Background

#6355 — "[Newton] Add a kitless training container" — installs through "${ISAACLAB_PATH}/isaaclab.sh" --install newton,rl[all],ov[ovrtx], matching Dockerfile.base and Dockerfile.curobo. That path goes through uv pip, which does not read uv.lock; there is no uv sync or --frozen left in the Dockerfile.

3. Details

uv.lock was still copied in the same layer as pyproject.toml. Nothing reads it, but a COPY makes a file part of the build cache key regardless, so every lockfile change invalidated that layer and forced a full dependency reinstall.

The workflow's change-detection pattern had the same problem in reverse: a lockfile-only change triggered a GPU build that could not produce a different image.

pyproject.toml and the per-package manifests still gate the build, which is what uv pip install --editable actually resolves from.

4. Test plan

• Confirmed nothing in isaaclab.sh, the install CLI, Dockerfile.kitless or validate-kitless-image reads uv.lock, uv sync, uv run or --frozen.
• docker/test/test_container_profiles.py + docker/test/test_dockerfile_nonroot.py: 30 passed.
• uv run isaaclab -f on all files.
• tools/changelog/cli.py check — no source/<pkg>/ touched, no fragment required.