Clean up internal clipboard handling

We now filter incoming data, which means we can start assuming the
clipboard data is always null terminated. This allows us to clean
up a lot of the internal handling.
diff --git a/common/rfb/InputHandler.h b/common/rfb/InputHandler.h
index 6c07284..b91f0e4 100644
--- a/common/rfb/InputHandler.h
+++ b/common/rfb/InputHandler.h
@@ -37,8 +37,7 @@
                           bool __unused_attr down) { }
     virtual void pointerEvent(const Point& __unused_attr pos,
                               int __unused_attr buttonMask) { }
-    virtual void clientCutText(const char* __unused_attr str,
-                               int __unused_attr len) { }
+    virtual void clientCutText(const char* __unused_attr str) { }
   };
 
 }