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](https://cs.opensource.google/fuchsia/fuchsia/+/main:tools/devshell/contrib/remove-update-source)