Fix plt.pause() behaviour (#291)

* Remove methods that call non-existing methods

* Update backend_nbagg.py

Author: thomasaarholt

ipympl/backend_nbagg.py

@@ -19,8 +19,7 @@
                                                      FigureCanvasWebAggCore,
                                                      NavigationToolbar2WebAgg,
                                                      TimerTornado)
-from matplotlib.backend_bases import (ShowBase, NavigationToolbar2,
-                                      FigureCanvasBase, cursors)
+from matplotlib.backend_bases import ShowBase, NavigationToolbar2, cursors
 
 from ._version import js_semver
 
@@ -242,12 +241,6 @@ def send_binary(self, data):
     def new_timer(self, *args, **kwargs):
         return TimerTornado(*args, **kwargs)
 
-    def start_event_loop(self, timeout):
-        FigureCanvasBase.start_event_loop_default(self, timeout)
-
-    def stop_event_loop(self):
-        FigureCanvasBase.stop_event_loop_default(self)
-
 
 class FigureManager(FigureManagerWebAgg):
     ToolbarCls = Toolbar