[BUG] Early stopping does not seem to work

The early stopping callback does not work as expected, and crashes at the end of
max_epochs with:

```
~/miniconda3/envs/py38/lib/python3.8/site-packages/pytorch_lightning/trainer/callback_hook.py in on_train_end(self)
    155         """Called when the train ends."""
    156         for callback in self.callbacks:
--> 157             callback.on_train_end(self, self.lightning_module)
    158
    159     def on_pretrain_routine_start(self) -> None:

~/work/repos/prototorch_models/prototorch/models/callbacks.py in on_train_end(self, trainer, pl_module)
     18     def on_train_end(self, trainer, pl_module):
     19         # instead, do it at the end of training loop
---> 20         self._run_early_stopping_check(trainer, pl_module)
     21
     22

TypeError: _run_early_stopping_check() takes 2 positional arguments but 3 were given
```

examples/dynamic_pruning.py

@@ -46,19 +46,27 @@ if __name__ == "__main__":
     vis = pt.models.VisGLVQ2D(train_ds)
     pruning = pt.models.PruneLoserPrototypes(
         threshold=0.01,  # prune prototype if it wins less than 1%
-        prune_after_epochs=30,  # pruning too early may cause problems
+        idle_epochs=30,  # pruning too early may cause problems
         prune_quota_per_epoch=1,  # prune at most 1 prototype per epoch
         frequency=5,  # prune every fifth epoch
         verbose=True,
     )
+    es = pt.models.EarlyStopWithoutVal(
+        monitor="loss",
+        min_delta=0.1,
+        patience=3,
+        mode="min",
+        verbose=True,
+    )
 
     # Setup trainer
     trainer = pl.Trainer.from_argparse_args(
         args,
-        max_epochs=100,
+        max_epochs=250,
         callbacks=[
             vis,
             pruning,
+            es,
         ],
         terminate_on_nan=True,
         weights_summary=None,