refactor(core): cleanup to match arm

src/arm_pkg/arm_pkg/arm_node.py

@@ -1,5 +1,4 @@
 import sys
-import threading
 import signal
 import math
 from warnings import deprecated
@@ -26,8 +25,6 @@ control_qos = qos.QoSProfile(
     # liveliness_lease_duration=Duration(seconds=5),
 )
 
-thread = None
-
 
 class ArmNode(Node):
     """Relay between Anchor and Basestation/Headless/Moveit2 for Arm related topics."""