Change popBackStackImmediate to popBackStack.

Fixes: 34801945

Immediate is no longer necessary since we don't reuse HistoryFragments.

Change-Id: Ieb31882df8e9c01b753f27f91aa9f0f70e219019
diff --git a/src/com/android/calculator2/Calculator.java b/src/com/android/calculator2/Calculator.java
index 5019fdf..b5901f9 100644
--- a/src/com/android/calculator2/Calculator.java
+++ b/src/com/android/calculator2/Calculator.java
@@ -731,8 +731,7 @@
     private void removeHistoryFragment() {
         final FragmentManager manager = getFragmentManager();
         if (manager != null && !manager.isDestroyed()) {
-            manager.popBackStackImmediate(HistoryFragment.TAG,
-                    FragmentManager.POP_BACK_STACK_INCLUSIVE);
+            manager.popBackStack(HistoryFragment.TAG, FragmentManager.POP_BACK_STACK_INCLUSIVE);
         }
 
         // When HistoryFragment is hidden, the main Calculator is important for accessibility again.