Revert "Fix Editor.current_editor buffer (for prompt_toolkit 2.0)."

This reverts commit 573c064.

Author: jonathanslenders

pyvim/editor.py

@@ -191,7 +191,13 @@ def current_editor_buffer(self):
         """
         Return the `EditorBuffer` that is currently active.
         """
-        return self.application.current_buffer
+        # For each buffer name on the focus stack.
+        for current_buffer_name in self.application.buffers.focus_stack:
+            if current_buffer_name is not None:
+                # Find/return the EditorBuffer with this name.
+                for b in self.window_arrangement.editor_buffers:
+                    if b.buffer_name == current_buffer_name:
+                        return b
 
     @property
     def add_key_binding(self):