Remove EventManager reset methods, because they violate encapsulation.

The whole idea of the EventManager is that you can register hooks
without worrying about what hooks other pieces of code might be
registering. The reset methods violate this separation of concerns,
since they will blow away everyone else's hooks too. (See gh-6680 for
an example of this breaking things.) Since there is never any safe way
to use them, we simply remove them entirely.

IPython/core/events.py

@@ -63,14 +63,6 b' class EventManager(object):'
         """Remove a callback from the given event."""
         self.callbacks[event].remove(function)
     
-    def reset(self, event):
-        """Clear all callbacks for the given event."""
-        self.callbacks[event] = []
-    
-    def reset_all(self):
-        """Clear all callbacks for all events."""
-        self.callbacks = {n:[] for n in self.callbacks}
-    
     def trigger(self, event, *args, **kwargs):
         """Call callbacks for ``event``.
         

IPython/core/tests/test_events.py

@@ -25,22 +25,8 b' class CallbackTests(unittest.TestCase):'
         self.em.trigger('ping_received')
         self.assertEqual(cb.call_count, 1)
     
-    def test_reset(self):
-        cb = Mock()
-        self.em.register('ping_received', cb)
-        self.em.reset('ping_received')
-        self.em.trigger('ping_received')
-        assert not cb.called
-    
-    def test_reset_all(self):
-        cb = Mock()
-        self.em.register('ping_received', cb)
-        self.em.reset_all()
-        self.em.trigger('ping_received')
-        assert not cb.called
-    
     def test_cb_error(self):
         cb = Mock(side_effect=ValueError)
         self.em.register('ping_received', cb)
         with tt.AssertPrints("Error in callback"):
-            self.em.trigger('ping_received')
  No newline at end of file
+            self.em.trigger('ping_received')

IPython/core/tests/test_interactiveshell.py

@@ -301,7 +301,10 b' class InteractiveShellTestCase(unittest.TestCase):'
             assert post_explicit.called
         finally:
             # remove post-exec
-            ip.events.reset_all()
+            ip.events.unregister('pre_run_cell', pre_explicit)
+            ip.events.unregister('pre_execute', pre_always)
+            ip.events.unregister('post_run_cell', post_explicit)
+            ip.events.unregister('post_execute', post_always)
     
     def test_silent_noadvance(self):
         """run_cell(silent=True) doesn't advance execution_count"""