Reverts default launch argument "capabilities" to not cause an error

[b-adkins]

Reverts capabilities default value to the empty string. Reverts #2696.

The issue is extensively documented:

• Launch Error #2734
• Pass along move_group_capabilities parameters (backport #2587) #2696

Description

Reverted the backport to the empty string, which it was before the merge that apparently broke things. Alternatively,

default_value=moveit_config.move_group_capabilities

was suggested in these discussions. Both worked on my system.

[github-actions]

This PR is stale because it has been open for 45 days with no activity. Please tag a maintainer for help on completing this PR, or close it if you think it has become obsolete.

[mergify]

Please target the main branch for development, we will backport the changes to humble for you if approved and if they don't break API.

[mikeferguson]

I would suggest we take #3018 instead of this at it fixes the issue but also keeps the "new" feature that was intended (and then back port it to humble/iron as well)