test-runner: don't reset dbus object on reset()

Doing this is redundant since the dbus object is initialized
anyways when a new test starts.

tools/test-runner

@@ -593,9 +593,6 @@ class Namespace:
 
 		self.radios = []
 
-		if self.name == "root":
-			self._bus = dbus.bus.BusConnection(address_or_type=self.dbus_address)
-
 		for p in list(self.processes):
 			print("Killing process %s" % p.name)
 			p.kill()