chore: remove rpc.rs

[jking-aus]

Description

rpc.rs should have been removed previously

Notes & open questions

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[jxs]

this file is actually required, it's not dangling,
lib.rs requires it

[michaelsproul]

I don't know what's going on with the diff here*, but rpc.rs is not used on the sigp-gossipsub branch:

rust-libp2p/protocols/gossipsub/src/lib.rs

Lines 97 to 114 in fabf27f

	mod backoff;
	mod behaviour;
	mod config;
	mod error;
	mod gossip_promises;
	mod handler;
	mod mcache;
	#[cfg(feature = "metrics")]
	mod metrics;
	mod peer_score;
	mod protocol;
	mod queue;
	mod rpc_proto;
	mod subscription_filter;
	mod time_cache;
	mod topic;
	mod transform;
	mod types;

i.e. commit fabf27f

*Related: I had a commit 5acdf89 checked out locally for sigp-gossipsub which is no longer on that branch, did it get force pushed out of existence? Maybe that's what messed up the diff for this PR.