COMP: remove reference to Mesh/index.rst in Core/index.rst
COMP: remove reference to Mesh/index.rst in Core/index.rst

Change-Id: If510473c7b3a8a195b35bf36364994befe4cecd5

InsightSoftwareConsortium/ITKExamples,InsightSoftwareConsortium/ITKExamples,InsightSoftwareConsortium/ITKExamples,InsightSoftwareConsortium/ITKExamples,InsightSoftwareConsortium/ITKExamples