Remove spiped for node_exporter metrics collection

[patrickod]

The inability to rename targets means that currently our prometheus targets for the various node_exporter processes are known to prometheus as localhost:910X as they connect using an spiped tunnel.

I don't think there's anything particularly sensitive about this information that would necessitate keeping this configuration. Removing it would allow us to more easily operate on all the metrics associated with a host, including both the blackbox probes and node metrics without having to deal with the mapping.