kivy: minor fixes

electrum/gui/kivy/__init__.py

@@ -60,3 +60,6 @@ class ElectrumGui:
                            plugins = self.plugins,
                            gui_object=self)
         w.run()
+
+    def stop(self):
+        pass

electrum/gui/kivy/uix/dialogs/lightning_open_channel.py

@@ -2,7 +2,6 @@ from kivy.lang import Builder
 from kivy.factory import Factory
 from electrum.gui.kivy.i18n import _
 from electrum.lnaddr import lndecode
-from electrum.gui.kivy.uix.dialogs.choice_dialog import ChoiceDialog
 from electrum.util import bh2u
 from electrum.bitcoin import COIN
 import electrum.simple_config as config