Remove support for sqlalchemy-migrate < 0.7
Remove support for sqlalchemy-migrate < 0.7

The sqlalchemy-migrate dependency already requires >= 0.7, so supporting
anything older is unnecessary

Change-Id: I0cfd640f420b4fe2837b496f4ef3d3e260619b63

sigmavirus24/glance,jumpstarter-io/glance,paramite/glance,jumpstarter-io/glance,akash1808/glance,akash1808/glance,JioCloud/glance,takeshineshiro/glance,wkoathp/glance,cloudbau/glance,rickerc/glance_audit,ntt-sic/glance,cloudbau/glance,ozamiatin/glance,JioCloud/glance,klmitch/glance,ntt-sic/glance,citrix-openstack-build/glance,citrix-openstack-build/glance,openstack/glance,vuntz/glance,redhat-openstack/glance,stevelle/glance,rajalokan/glance,kfwang/Glance-OVA-OVF,dims/glance,kfwang/Glance-OVA-OVF,openstack/glance,vuntz/glance,scripnichenko/glance,tanglei528/glance,scripnichenko/glance,darren-wang/gl,wkoathp/glance,paramite/glance,SUSE-Cloud/glance,dims/glance,tanglei528/glance,rickerc/glance_audit,redhat-openstack/glance,rajalokan/glance,openstack/glance,klmitch/glance,darren-wang/gl,saeki-masaki/glance,sigmavirus24/glance,takeshineshiro/glance,stevelle/glance,ozamiatin/glance,SUSE-Cloud/glance,saeki-masaki/glance