Remove unnecessary virDomainDefClearDeviceAliases

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.