Remove tainted zeroing from packDomainName

With the label copying now moved after the compression, the msg buffer
will no longer be tainted and need clearing.

msg.go

@@ -307,12 +307,6 @@ loop:
 	}
 	// If we did compression and we find something add the pointer here
 	if pointer != -1 {
-		// Clear the msg buffer after the pointer location, otherwise
-		// packDataNsec writes the wrong data to msg.
-		tainted := msg[nameoffset:off]
-		for i := range tainted {
-			tainted[i] = 0
-		}
 		// We have two bytes (14 bits) to put the pointer in
 		// if msg == nil, we will never do compression
 		binary.BigEndian.PutUint16(msg[nameoffset:], uint16(pointer^0xC000))