Remove DEVSTACK_GATE_TIMEOUT setting

We do not need to set this variable anymore, remove a stray version of
it. This was introduced as part of
I4e01e39d3113547002fffc094e38f1f395b16818 and not updated when we
remove DEVSTACK_GATE_TIMEOUT everywhere.

Change-Id: Ia629033eed9a8160103831e90bb4c81d36dccff3

jenkins/jobs/cinder.yaml

@@ -54,7 +54,6 @@
       - shell: |
           #!/bin/bash -xe
           export PYTHONUNBUFFERED=true
-          export DEVSTACK_GATE_TIMEOUT=60
           export BRANCH_OVERRIDE={branch-override}
           export PROJECTS="openstack/python-brick-cinderclient-ext $PROJECTS"
           export DEVSTACK_PROJECT_FROM_GIT=python-brick-cinderclient-ext