Removes fixed timestep env for runtime (#297)

# Description

Remove the fixed time step flag `NV_PACER_FIXED_TIME_STEP_MS` for
CloudXR runtime container.

## Type of change

- Bug fix (non-breaking change which fixes an issue)


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## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

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docker/docker-compose.cloudxr-runtime.patch.yaml

@@ -18,7 +18,6 @@ services:
       start_period: 5s
     environment:
       - ACCEPT_EULA=${ACCEPT_EULA}
-      - NV_PACER_FIXED_TIME_STEP_MS=32
     volumes:
       - openxr-volume:/openxr:rw