revert: remove apt/dpkg workarounds from #388 and #389

[naincy128]

Jira: LP-1289

Description

Reverts two earlier attempts to fix the stage-xqueue failure at TASK [security : Take security updates during ansible runs]:

• fix: wait for background apt/dpkg before running unattended-upgrade #388 – wait for background apt/dpkg to release the dpkg lock, and delay: 30 on retries (shared security role)
• fix: repair apt state before security updates in xqueue playbook #389 – apt-repair pre_tasks in playbooks/xqueue.yml

Neither change fixed the failure. Deploys kept failing after both were merged. The cause was unattended-upgrade refusing to upgrade packages whose conffile had been modified locally ("conffile prompt"). #391 fixed that, and the pipeline has been green since.

Changes

• playbooks/xqueue.yml: remove the apt-repair pre_tasks block. The file is back to how it was before fix: repair apt state before security updates in xqueue playbook #389.
• playbooks/roles/security/tasks/security-ubuntu.yml: remove the "Wait for background apt/dpkg to release the dpkg lock" task and the delay: 30 on the security-update retries.