plugin.sh: Remove setting of os_privileged_user_* params
plugin.sh: Remove setting of os_privileged_user_* params

devstack with commit 38bee18a2c440b01bd1c2187cb2a62a841e3b7ae
added support for configuring os_privileged_user_* params so
we don't need to do it in our plugin code.

Change-Id: I4827d92acba4f4e960177bc76524d94ce0b58095

stackforge/devstack-plugin-glusterfs,stackforge/devstack-plugin-glusterfs