Dev: sbd: Remove sbd configuration directories while removing cluster node

[liangxin1300]

Problem

As noted in #1953, after removing a cluster node, the directories /etc/systemd/system/sbd.service.d and /run/systemd/system/sbd.service.d are left behind.

Changes

• Ensure both directories are removed when a cluster node is removed.
• Refactor the cleanup logic into a new function, sbd.cleanup_sbd_configurations, which is now invoked during both cluster remove <node> and sbd purge subcommands

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.75%. Comparing base (9d10628) to head (080b36e).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
integration	55.18% <23.07%> (-0.01%)	⬇️
unit	52.92% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
crmsh/bootstrap.py	87.85% <100.00%> (-0.01%)	⬇️
crmsh/sbd.py	83.98% <100.00%> (+0.08%)	⬆️

... and 1 file with indirect coverage changes

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