Remove IRB2400 IKFast plugin

[marip8]

I've been attempting to use the IRB2400 IKFast plugin to test a different plugin that I've been working on recently, and it seems like there are a few outstanding issues with the IRB2400 IKFast MoveIt plugin which might merit its removal from this repository

1. Per irb2400 IKFast plugin doesn't match URDF #80, it may not actually match the geometry of the URDF. It doesn't seem like anyone has checked this out in a number of years to confirm
2. The getPositionFK function always returns false for me (Ubuntu 16.04, ROS Kinetic) because it checks #ifndef IKTYPE_TRANSFORM_6D, which according to this issue seems to have been removed/deprecated

Rather than fixing this plugin, I suggest we remove it in favor of using moveit_opw_kinematics_plugin, which is significantly easier to set up and has faster performance for this type of IK problem than IKFast (if I remember correctly from earlier benchmarking of opw_kinematics)

[gavanderhoorn]

While I agree the problem should be addressed, we cannot just remove the package in kinetic-devel, as it has been released into both Kinetic and Melodic.

Removal could target a noetic-devel (which doesn't exist yet).

However that doesn't help us here in kinetic-devel.

I'll see if I can generate a new version of the IKFast plugin. Then we can merge that, remove in noetic-devel and migrate to something else.

I suggest we remove it in favor of using moveit_opw_kinematics_plugin

that would indeed be a good idea, but moveit_opw_kinematics_plugin has to be released before we do this.

We cannot ask all users of the packages here to build them from source.

[marip8]

I wasn't exactly sure what the implications are for released packages, but that makes sense. I'll close this PR and we can address it for Noetic.