devmapper: Remove unnecessary call to allocateTransactionId() during device removal

Remove call to allocateTransactionId() during device removal. This seems to
be unnecessary and it is not clear what this call is doing.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

daemon/graphdriver/devmapper/deviceset.go

@@ -793,7 +793,6 @@ func (devices *DeviceSet) deleteDevice(info *DevInfo) error {
 		return err
 	}
 
-	devices.allocateTransactionId()
 	devices.devicesLock.Lock()
 	delete(devices.Devices, info.Hash)
 	devices.devicesLock.Unlock()