[discovery] Remove redundant discovery.receiver.rule attribute

[dmitryax]

Do not report discovery.receiver.rule resource attribute with entities and metrics. It's not being used.

[hughesjj]

Exporting failed. Will retry the request after interval. {"kind": "exporter", "name": "signalfx", "error": "Post "[https://ingest.test.signalfx.com/v2/datapoint](https://ingest.test.signalfx.com/v2/datapoint/)": dial tcp: lookup ingest.test.signalfx.com on 168.63.129.16:53: no such host", "interval": "4.688570936s"}
sh: pgrep: command not found

Running 'sh -ec 'systemctl status splunk-otel-collector && pgrep -a -u splunk-otel-collector -f /usr/bin/otelcol'' ...

Issue with pgrep, either not on path or binary not on device. Likely unrelated to the this change