Implement predictive back navigation in ModelFieldEditor

Simply deleted the onBackPressed() callback as all it did was to close
the activity. Without a back callbak set, the system will handle the
back navigation itself.

The toolbar home button was already handled in the superclass AnkiActivity.

AnkiDroid/src/main/java/com/ichi2/anki/ModelFieldEditor.kt

@@ -454,10 +454,6 @@ class ModelFieldEditor : AnkiActivity(), LocaleSelectionDialogHandler {
     }
 
     override fun onOptionsItemSelected(item: MenuItem): Boolean = when (item.itemId) {
-        android.R.id.home -> {
-            onBackPressed()
-            true
-        }
         R.id.action_add_new_model -> {
             addFieldDialog()
             true
@@ -469,12 +465,6 @@ class ModelFieldEditor : AnkiActivity(), LocaleSelectionDialogHandler {
         finishWithAnimation(ActivityTransitionAnimation.Direction.END)
     }
 
-    @Suppress("DEPRECATION", "Deprecated in API34+dependencies for predictive back feature")
-    override fun onBackPressed() {
-        super.onBackPressed()
-        closeActivity()
-    }
-
     fun handleAction(contextMenuAction: ModelEditorContextMenuAction) {
         when (contextMenuAction) {
             ModelEditorContextMenuAction.Sort -> sortByField()