Unregister broadcast receiver when QC is destroyed

- There will be OutOfMemoryError w/o doing so.

Bug: 33203761

Test: manually verified it doesn't crash following steps to
      repro in http://b/33203761#comment5

Change-Id: I02f8cd46cfef8681b234bbed5921fe62b4581acc
diff --git a/src/com/android/contacts/quickcontact/QuickContactActivity.java b/src/com/android/contacts/quickcontact/QuickContactActivity.java
index 81a3741..fcd0a50 100644
--- a/src/com/android/contacts/quickcontact/QuickContactActivity.java
+++ b/src/com/android/contacts/quickcontact/QuickContactActivity.java
@@ -2560,6 +2560,7 @@
 
     @Override
     public void onDestroy() {
+        LocalBroadcastManager.getInstance(this).unregisterReceiver(mListener);
         super.onDestroy();
     }