shutdown_requested Should not be Abstract (#57)

Existing users should be able to upgrade the library without issues.
Removed the abstract decorator to ensure that existing users'
applications continue to work normally.

Author: pfifer

amazon_kclpy/kcl.py

@@ -220,7 +220,6 @@ def shutdown(self, checkpointer, reason):
         '''
         raise NotImplementedError
 
-    @abc.abstractmethod
     def shutdown_requested(self, checkpointer):
         """
         Called by a KCLProcess instance to indicate that this record processor is about to be be shutdown.  This gives

amazon_kclpy/v2/processor.py

@@ -73,7 +73,6 @@ def shutdown(self, shutdown_input):
         """
         raise NotImplementedError
 
-    @abc.abstractmethod
     def shutdown_requested(self, shutdown_requested_input):
         """
         Called by a KCLProcess instance to indicate that this record processor is about to be be shutdown.  This gives