filedaemon: remove ovirt plugin

[pstorz]

Thank you for contributing to the Bareos Project!

This PR removes the oVirt plugin.

Bareos dropped the support for Python 2, and the oVirt Plugin does not work stable on Python 3.

As Red Hat already has announced that Red Hat Virtualization will be
discontinued and customers should merge away, the Bareos project will not
work on solving the problems with Python 3 which are caused by third-party
python modules.

If you are using the oVirt plugin, stay with Baros 22 using the Python 2
Version of the plugin.

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[bruno-at-bareos]

I would like to propose to remove the rest of the documentation chapter, especially for 24,23 so people going to look for a detail will see that it doesn't exist anymore.

We can backport to 22 the warning section. and as you wish keep just that warning in 23 documentation and remove everything in master.

We will keep the o-virt filter in the subscription view for still a few version, as it may help to determined usage of obsolete plugins.

To be checked in core/cmake/BareosInstallConfigFiles.cmake:153 there's a mention of o-virt.