Cleanup for BottomActionBar

- Remove the duplicated API, we don't need two same APIs.
- Remove the duplicated back key binding, since it's done in BottomActionBarFragment.

Test: Manually
Bug: 155157385
Change-Id: I682ebe67f5b7187a1434960d553063b8c6f9d3f6
diff --git a/src/com/android/customization/picker/grid/GridFullPreviewFragment.java b/src/com/android/customization/picker/grid/GridFullPreviewFragment.java
index 68ecc5b..2be77d6 100644
--- a/src/com/android/customization/picker/grid/GridFullPreviewFragment.java
+++ b/src/com/android/customization/picker/grid/GridFullPreviewFragment.java
@@ -137,7 +137,6 @@
 
     @Override
     protected void onBottomActionBarReady(BottomActionBar bottomActionBar) {
-        bottomActionBar.bindBackButtonToSystemBackKey(getActivity());
         bottomActionBar.showActionsOnly(APPLY);
         bottomActionBar.setActionClickListener(APPLY, v -> finishActivityWithResultOk());
         bottomActionBar.show();
diff --git a/src/com/android/customization/picker/theme/ThemeFragment.java b/src/com/android/customization/picker/theme/ThemeFragment.java
index 84705c2..5528adb 100644
--- a/src/com/android/customization/picker/theme/ThemeFragment.java
+++ b/src/com/android/customization/picker/theme/ThemeFragment.java
@@ -165,7 +165,6 @@
     @Override
     protected void onBottomActionBarReady(BottomActionBar bottomActionBar) {
         mBottomActionBar = bottomActionBar;
-        mBottomActionBar.bindBackButtonToSystemBackKey(getActivity());
         mBottomActionBar.showActionsOnly(APPLY);
         mBottomActionBar.setActionClickListener(APPLY, v -> applyTheme());
     }