leave proximity enabled as long as CallViewController exists

Signal/src/ViewControllers/CallViewController.swift

@@ -157,6 +157,7 @@ class CallViewController: OWSViewController, CallObserver, CallServiceObserver,
 
     deinit {
         NotificationCenter.default.removeObserver(self)
+        self.proximityMonitoringManager.remove(lifetime: self)
     }
 
     @objc func didBecomeActive() {
@@ -170,9 +171,6 @@ class CallViewController: OWSViewController, CallObserver, CallServiceObserver,
     override func viewDidDisappear(_ animated: Bool) {
         super.viewDidDisappear(animated)
 
-        self.proximityMonitoringManager.remove(lifetime: self)
-        UIDevice.current.isProximityMonitoringEnabled = false
-
         callDurationTimer?.invalidate()
         callDurationTimer = nil
     }