SendableRegistry Add/AddLW/AddChild are broken

[virtuald]

They are trying to use keep alives to keep the pointers alive but it's not the right solution.

Probably need to do the same thing we do for SmartDashboard with a separate hash map to hold references.

import wpilib
import wpilib.drive
import wpiutil

leftLeader = wpilib.PWMSparkMax(1)
rightLeader = wpilib.PWMSparkMax(2)
drive = wpilib.drive.DifferentialDrive(
            leftLeader,
            rightLeader,
        )

wpiutil.SendableRegistry.addChild(drive, leftLeader)

$ python ../../t.py 
Traceback (most recent call last):
  File "../../t.py", in <module>
    wpiutil.SendableRegistry.addChild(drive, leftLeader)
RuntimeError: Could not activate keep_alive!