Remove VALID_USERNAME regex from utils.py
Remove VALID_USERNAME regex from utils.py

The corresponding util function was moved to coaster.Utils

hasgeek/funnel,hasgeek/funnel,hasgeek/lastuser,hasgeek/funnel,hasgeek/lastuser,hasgeek/lastuser,hasgeek/funnel,hasgeek/lastuser,hasgeek/lastuser,hasgeek/funnel