Remove enabling of glance v1 API

devstack removing the glance v1 api enable
option[1] because there is no v1 entry point in glance
now[2].

Let's remove ths GLANCE_V1_ENABLED variable setting from
zuul job too to avoid any confusion of glance v1 is still
available.
[1] https://review.opendev.org/#/c/698808/
[2] https://review.opendev.org/#/c/532503/

Change-Id: I6d3a38eee0c75bbc795bad732fe547181d15c677

Author: Ghanshyam Mann

.zuul.yaml

@@ -51,8 +51,6 @@
     vars:
       devstack_localrc:
         LIBS_FROM_GIT: python-openstackclient
-        # NOTE(dtroyer): OSC needs to support Image v1 for a while yet so re-enable
-        GLANCE_V1_ENABLED: true
         # NOTE(dtroyer): Functional tests need a bit more volume headroom
         VOLUME_BACKING_FILE_SIZE: 20G
       devstack_local_conf: