Fixed minor typo causing AttributeError to be thrown.
Removing unused code in the notebook MappingKernelManager.

This cleans up the API for restarts in the notebook's kernel
manager classes.
Merge pull request #2773 from dhirschfeld/typo-fix

Fixed minor typo causing AttributeError to be thrown.
Merge pull request #2774 from ellisonbg/kernelrestart

Removing unused code in the notebook MappingKernelManager.