pass Pubkeys as refs, copy only where values needed (#3213)

* pass Pubkeys as refs, copy only where values needed

* Pubkey is pervasive

* fixup

core/src/test_tx.rs

@@ -7,5 +7,5 @@ pub fn test_tx() -> Transaction {
     let keypair1 = Keypair::new();
     let pubkey1 = keypair1.pubkey();
     let zero = Hash::default();
-    SystemTransaction::new_account(&keypair1, pubkey1, 42, zero, 0)
+    SystemTransaction::new_account(&keypair1, &pubkey1, 42, zero, 0)
 }