Do not log passphrase length to STDOUT

src/mainwindow.cpp

@@ -567,7 +567,7 @@ void MainWindow::removeWalletEncryption() {
 
     int length = passphrase.length();
 
-    qDebug() << __func__ << ": Passphrase length = " << length;
+    // qDebug() << __func__ << ": Passphrase length = " << length;
 
     char *sequence = NULL;
     sequence = new char[length+1];