Bug 1551738: [release] Removed unsued channel from secondary-update-verify tasks.

a17faa0e5bf8f1680c750e81a5424715a7825387 switchted to pulling the channel from
the update-verify-config task, and missed removing the setting for
secondary-update-verify.

Differential Revision: https://phabricator.services.mozilla.com/D31512

--HG--
extra : moz-landing-system : lando

taskcluster/ci/release-secondary-update-verify/kind.yml

@@ -31,8 +31,6 @@ job-defaults:
         max-run-time: 7200
         retry-exit-status:
             - 255
-        env:
-            CHANNEL: "beta-localtest"
     treeherder:
         symbol: UV(UVS)
         kind: test