Fix remove_attached_object API in Python PSI, add clear()

[felixvd]

Setting the link name in remove_attached_object is not necessary. planning_scene.cpp treats the message as described.

I also added a clear() method because I could have used it today and saw that @mikeferguson also did in moveit_python.

[v4hn]

It's a useful abstraction, but it would be nicer to expose this API as sending a single PlanningScene message.
It's just stupid overhead that can even show in Rviz (the attached objects might actually detach in RViz before being removed).
It looks like the asynchronous backend of the class does not even have a publisher to planning_scene at the moment...

[v4hn]

Looks good to me. CI failed for seemingly unrelated reasons, I restarted the job.

Please consider my inline comment though.

[codecov]

Codecov Report

Merging #2609 (c5505b4) into master (3a61f18) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2609      +/-   ##
==========================================
- Coverage   60.49%   60.48%   -0.01%     
==========================================
  Files         402      402              
  Lines       29611    29611              
==========================================
- Hits        17911    17908       -3     
- Misses      11700    11703       +3     

Impacted Files	Coverage Δ
.../ompl_interface/src/detail/constrained_sampler.cpp	43.25% <0.00%> (-16.21%)	⬇️
...meterization/work_space/pose_model_state_space.cpp	82.06% <0.00%> (-1.92%)	⬇️
...raint_samplers/src/default_constraint_samplers.cpp	83.89% <0.00%> (-0.32%)	⬇️
...e/collision_detection_fcl/src/collision_common.cpp	78.61% <0.00%> (+0.26%)	⬆️
...nning_scene_monitor/src/planning_scene_monitor.cpp	68.68% <0.00%> (+0.55%)	⬆️
...ipulation/pick_place/src/manipulation_pipeline.cpp	73.79% <0.00%> (+1.95%)	⬆️

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[rhaschke]

I can only support Michael's review. +1

[felixvd]

Thanks for the reviews. I agree that there are things to be improved in the backend (a CLEAR_ALL command, a DETACH command separate from REMOVE...), but I prefer not to go that far down the rabbit hole right now.