Hide hardware cursor completely via "cursor: none" on browsers that support it.

guacamole/src/main/webapp/styles/client.css

@@ -31,6 +31,7 @@ img {
 .software-cursor {
     cursor: url('../images/mouse/dot.gif'),url('../images/mouse/blank.cur'),default;
     overflow: hidden;
+    cursor: none;
 }
 
 .guac-error .software-cursor {