[TrivialFix] Remove redundant function in RbacUtils class

This commit simply removes a redundant functionf rom RbacUtils class
that shouldn't have been merged. get_roles was renamed to
get_roles_by_name and because both now exist get_roles should be
removed.

Change-Id: I659d6f5f511d3bd47be05ed27990f4ee55886682
1 file changed