fix a compilation warning (#6279)

Fixes #6277.

polkadot/Cargo.toml

@@ -126,7 +126,6 @@ maintenance = { status = "actively-developed" }
 # This list is ordered alphabetically.
 [profile.dev.package]
 blake2 = { opt-level = 3 }
-blake2-rfc = { opt-level = 3 }
 blake2b_simd = { opt-level = 3 }
 chacha20poly1305 = { opt-level = 3 }
 cranelift-codegen = { opt-level = 3 }