SystemUI: Avoid NPEs during status bar recreation for MSIM

PS2:
   * Clear the subs views on recreation
   * Unregister receivers on recreation

Change-Id: Id131ffac497f46a753a97b479823e51fda7c412c
(cherry picked from commit 5744ab14573a405af0f13f7e198330abbad5f9f1)

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBar.java