[ci] Remove defend workflows on serverless

These shouldn't be running on 8.x

.buildkite/pipelines/pull_request/security_solution/defend_workflows.yml

@@ -18,20 +18,3 @@ steps:
       automatic:
         - exit_status: '-1'
           limit: 1
-
-  - command: .buildkite/scripts/steps/functional/defend_workflows_serverless.sh
-    label: 'Defend Workflows Cypress Tests on Serverless'
-    agents:
-      enableNestedVirtualization: true
-      localSsds: 1
-      localSsdInterface: nvme
-      machineType: n2-standard-4
-    depends_on:
-      - build
-      - quick_checks
-    timeout_in_minutes: 60
-    parallelism: 14
-    retry:
-      automatic:
-        - exit_status: '-1'
-          limit: 1