removed not needed dipendency for persy feature

Cargo.toml

@@ -89,7 +89,7 @@ thread_local = "1.1.3"
 [features]
 default = ["conduit_bin", "backend_sqlite"]
 backend_sled = ["sled"]
-backend_persy = ["persy","num_cpus"]
+backend_persy = ["persy"]
 backend_sqlite = ["sqlite"]
 backend_heed = ["heed", "crossbeam"]
 sqlite = ["rusqlite", "parking_lot", "crossbeam", "tokio/signal"]