Get rid of the register mechanism for encoders and decoders

We have no use for it, so let's keep things simple.
diff --git a/common/rfb/RREDecoder.h b/common/rfb/RREDecoder.h
index 2309f75..98abf98 100644
--- a/common/rfb/RREDecoder.h
+++ b/common/rfb/RREDecoder.h
@@ -24,11 +24,10 @@
 
   class RREDecoder : public Decoder {
   public:
-    static Decoder* create(CMsgReader* reader);
-    virtual void readRect(const Rect& r, CMsgHandler* handler);
-    virtual ~RREDecoder();
-  private:
     RREDecoder(CMsgReader* reader);
+    virtual ~RREDecoder();
+    virtual void readRect(const Rect& r, CMsgHandler* handler);
+  private:
     CMsgReader* reader;
   };
 }