This removes the very old glance config options which were deprecated
in I9054bcfb7f5a4a31f0bbfd770c00c767f3d165ba in favor of
glance.api_servers config option. This is required to clear out any
default glance servers so that we could pull from the service catalog
as a default in the future.
Change-Id: Ie2d767c4422ef339d6dcb826f3c8ba3c7cf79f85