remove deprecated netinterface monitor

[atoulme]

Description:

This removes the deprecated netinterface monitor. This component was deprecated 3 years 9 months ago. As noted in the documentation of this monitor, the net-io monitor should be used instead:

    **This monitor is deprecated in favor of the `net-io` monitor. Please
    switch to that monitor as this monitor will be removed in a future release
    of the agent.**  Note that the `net-io` monitor uses the `interface`
    dimension to identify the network card instead of the `plugin_instance`
    dimension, but otherwise the metrics are the same.

[rmfitzpatrick]

please replace w/ deprecation notice for at least a release

notice added