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/RawDecoder.h b/common/rfb/RawDecoder.h
index 9fdbb22..e09cca2 100644
--- a/common/rfb/RawDecoder.h
+++ b/common/rfb/RawDecoder.h
@@ -24,11 +24,10 @@
 
   class RawDecoder : public Decoder {
   public:
-    static Decoder* create(CMsgReader* reader);
-    virtual void readRect(const Rect& r, CMsgHandler* handler);
-    virtual ~RawDecoder();
-  private:
     RawDecoder(CMsgReader* reader);
+    virtual ~RawDecoder();
+    virtual void readRect(const Rect& r, CMsgHandler* handler);
+  private:
     CMsgReader* reader;
   };
 }