Fix comment slashes in license

For some reason, the license was commented with 4 slashes in a couple
places. This changes it to the correct 2 slashes.
Merge branch 'fix/license-slashes' into 'master'

Fix comment slashes in some source files license

+1: Julien Lenoir, Harald Scheirich

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/1309463