COMP: Remove WebGLExport module from Slicer core - Will be distributed as extension.

See https://github.com/xtk/SlicerWebGLExport/pull/2

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21638 3bd1e089-480b-0410-8dfb-8563597acbee