mon: fix mon scaledown when mons are portable (backport #14106)

[mergify[bot]]

in case of portable mons, mon scaledown was skipped with below code

if mon.NodeName == "" {
            logger.Debugf("mon %q is not scheduled to a specific host", mon.DaemonName)
            continue
        }

which skips mon removal if mon nodeName is empty but if mons are scale down in case of portable mons in that case also we want to remove extra mons to match the cephCluster configuration.

Checklist:

• [ ] Commit Message Formatting: Commit titles and messages follow guidelines in the developer guide.
• [ ] Reviewed the developer guide on Submitting a Pull Request
• [ ] Pending release notes updated with breaking and/or notable changes for the next minor release.
• [ ] Documentation has been updated, if necessary.
• [ ] Unit tests have been added, if necessary.
• [ ] Integration tests have been added, if necessary.

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  This is an automatic backport of pull request #14106 done by Mergify.