Update admittance_controller to use shared 6D robot description

[naitikpahwa18]

Description

Updates admittance_controller to use the 6D robot description from ros2_control_test_assets package instead of maintaining a local copy.

Related Issues

Fixes #450

Changes

• Updated include path in test_admittance_controller.hpp to use ros2_control_test_assets/test_asset_6d_robot_description.hpp
• Removed local copy of test_asset_6d_robot_description.hpp from admittance_controller/test/
• Temporarily updated ros2_controllers.rolling.repos to point to my ros2_control PR branch for CI testing (will be reverted before merge)

Additional context

This PR should be merged in coordination with ros-controls/ros2_control#3032

[Copilot]

Pull request overview

This PR updates admittance_controller tests to consume the shared 6D robot URDF/SRDF description from the ros2_control_test_assets package, removing the duplicated local copy.

Changes:

• Switched test_admittance_controller.hpp to include ros2_control_test_assets/test_asset_6d_robot_description.hpp.
• Removed the local admittance_controller/test/test_asset_6d_robot_description.hpp copy.
• Updated ros2_controllers.rolling.repos to reference a ros2_control feature branch for CI testing.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
ros2_controllers.rolling.repos	Temporarily pins ros2_control dependency to a feature branch for CI validation.
admittance_controller/test/test_asset_6d_robot_description.hpp	Removes duplicated 6D robot description header from this package.
admittance_controller/test/test_admittance_controller.hpp	Uses the shared ros2_control_test_assets 6D robot description header.

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[Copilot]

ros2_controllers.rolling.repos is now pinned to a feature branch (move-6d-robot-450). Since this file is used by others to reproduce/consume the rolling source workspace, it should not reference a temporary PR branch; please revert this back to master (or a specific released tag/commit) before merging and rely on CI overrides for temporary testing.

[naitikpahwa18]

This was done temporarily as suggested by @christophfroehlich so the semi-binary builds can pick up the ros2_control branch. I’ll revert it back to master before merging.