Fix comment

We switched testnet to follow standard rules in zcash/zcash#1604, in
order to find bugs such as the one fixed in the previous commit.

src/main.cpp

@@ -1787,7 +1787,7 @@ bool AcceptToMemoryPool(
     if (tx.IsCoinBase())
         return state.DoS(100, false, REJECT_INVALID, "coinbase");
 
-    // Rather not work on nonstandard transactions (unless -testnet/-regtest)
+    // Rather not work on nonstandard transactions (unless -regtest)
     string reason;
     if (chainparams.RequireStandard() && !IsStandardTx(tx, reason, chainparams, nextBlockHeight))
         return state.DoS(0, false, REJECT_NONSTANDARD, reason);