tests: Reduce usage of legacy PCI controllers on PCIe machines
    
    Up until a while ago, libvirt would automatically add a legacy
    PCI controllers combo (dmi-to-pci-bridge + pci-bridge) to any
    PCIe machine type (x86_64/q35 and aarch64/virt).
    
    As a result, a number of input and output files in the test
    suite ended up containing the legacy PCI controllers, even
    though they are not needed or in any way relevant to the
    feature being tested.
    
    Get rid of most of the occurrences. Most of the time, this
    just means removing the controllers from the input file and
    regenerating the output files; in a few instances, some
    minor tweaking is performed on the input file, most notably
    removing the memory balloon: as memory balloon support was
    not the scope of the test being changed, there is no loss
    of test coverage from doing so.
    
    Several occurrences of the legacy PCI controllers remain in
    the test suite, both because removing their usage would have
    required even more tweaking, and because we still want to
    have coverage of this perfectly valid combination.