domain: Remove pre-startup USB collision check

Libvirt nowadays will throw an explicit warning about this
exact situation. It doesn't guide people to virt-manager UI, but
then again it should be obscure enough that it doesn't warrant this
special corner case code to inform the user

virtManager/domain.py

@@ -177,7 +177,6 @@ class vmmDomain(vmmLibvirtObject):
     __gsignals__ = {
         "resources-sampled": (vmmLibvirtObject.RUN_FIRST, None, []),
         "inspection-changed": (vmmLibvirtObject.RUN_FIRST, None, []),
-        "pre-startup": (vmmLibvirtObject.RUN_FIRST, None, [object]),
     }
 
     def __init__(self, conn, backend, key):
@@ -228,39 +227,6 @@ class vmmDomain(vmmLibvirtObject):
             # is blacklisted.
             raise RuntimeError("Can't track Domain-0 as a vmmDomain")
 
-        self.connect("pre-startup", self._prestartup_nodedev_check)
-
-    def _prestartup_nodedev_check(self, src, ret):
-        ignore = src
-        error = _("There is more than one '%s' device attached to "
-                  "your host, and we can't determine which one to "
-                  "use for your guest.\n"
-                  "To fix this, remove and reattach the USB device "
-                  "to your guest using the 'Add Hardware' wizard.")
-
-        usb_nodedevs = self.conn.filter_nodedevs("usb_device")
-
-        for hostdev in self.xmlobj.devices.hostdev:
-            devtype = hostdev.type
-
-            if devtype != "usb":
-                continue
-
-            vendor = hostdev.vendor
-            product = hostdev.product
-            bus = hostdev.bus
-            device = hostdev.device
-
-            if not vendor or not product:
-                continue
-
-            count = len([d for d in usb_nodedevs if
-                         (d.xmlobj.vendor_id == vendor and
-                          d.xmlobj.product_id == product)])
-            if count > 1 and not (bus and device):
-                prettyname = "%s %s" % (vendor, product)
-                ret.append(error % prettyname)
-
 
     ###########################
     # Misc API getter methods #
@@ -1317,13 +1283,6 @@ class vmmDomain(vmmLibvirtObject):
         if self.get_cloning():
             raise RuntimeError(_("Cannot start guest while cloning "
                                  "operation in progress"))
-
-        pre_startup_ret = []
-        self.emit("pre-startup", pre_startup_ret)
-
-        for error in pre_startup_ret:
-            raise RuntimeError(error)
-
         self._backend.create()
 
     @vmmLibvirtObject.lifecycle_action