Remove unnecessary virDomainDefClearDeviceAliases
    
    Nothing in the code path after the removed call has needs/uses the alias
    anyway (as would be the case for command line building or talking to monitor).
    The alias is VIR_FREE'd in virDomainDeviceInfoClear which is called for any
    device that needs/uses an alias via virDomainDeviceDefFree or virDomainDefFree
    as well as during virDomainDeviceInfoFree for host devices.
    
    For persistent domains, the domain definition (including aliases) gets
    freed a few screens later when it's replaced with newDef.
    
    For transient domains, the definition is freed/unref'd along with the
    virDomainObj a few moments later.