unregister a repository package server as a device's update source
usage: fx remove-update-source [--repo-name NAME]
Removes the repository as an update source on the target device.
--repo-name NAME Name of the repository package server to use as the update source.
NAME:
If no name is supplied, the name defaults to configured default repository.
Note:
This is a wrapper for `ffx target repository deregister`
remove-update-source source code