qemu: capabilities: Remove QEMU_CAPS_PIIX4_ACPI_HOTPLUG_BRIDGE

qemu: capabilities: Remove QEMU_CAPS_PIIX4_ACPI_HOTPLUG_BRIDGE

Commit 58ba0f6a3d7342fba29edbbf2bb9cb5497c870e5 added a capability which
is supported by all qemu versions we support. Remove it and the
associated dead code. Since the capability isn't present in any upstream
release we can delete it completely.

Specifically the commit itself states that it was introduced "around
(qemu) 2.1". The rest of the code handles properly that the feature is
used only on x86 with the i440fx machine so the capability is pointless.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>