Update libfuzzer-sys to new upstream inclusion method

Dunno why they changed it, but the old "depend directly on git"
thing that cargo-fuzz used forever is now deprecated that that
repo is archived, they've now moved to another repo and publish
properly on crates.io.

Author: TheBlueMatt

fuzz/Cargo.toml

@@ -23,7 +23,7 @@ lightning-rapid-gossip-sync = { path = "../lightning-rapid-gossip-sync" }
 bitcoin = { version = "0.28.1", features = ["secp-lowmemory"] }
 hex = "0.3"
 honggfuzz = { version = "0.5", optional = true }
-libfuzzer-sys = { git = "https://github.com/rust-fuzz/libfuzzer-sys.git", optional = true }
+libfuzzer-sys = { version = "0.4", optional = true }
 
 [build-dependencies]
 cc = "1.0"