Trim description suffixes

[stephane-caron]

Currently all description names end in _description for URDF and _mj_description for MJCF descriptions.

• Proposal: remove these suffixes.
• Pros: shorter description names, separate
• Cons: not matching any more for existing packages that are named <robot>_description
• Alternatives: status quo

[drfenixion]

How i remember i do parsing of code for grab data of packages from repo for RobotCAD library. It nice to not modify status quo or lt will lead to work to adapt parser.