ENH: Remove unnecessary templated code from tubeShortestPathKernel

This private function is only ever used with integers so simplify things by
removing the templated code, therefore removing the need for a cppcheck
suppression.

Change-Id: I96e09e5aa7b1197c1dbd929fdb4785ce9d48aecf
Merge topic 'RemoveTemplateFromEnsureOrder'

a6d9a66 ENH: Remove unnecessary templated code from tubeShortestPathKernel