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/RREEncoder.h b/common/rfb/RREEncoder.h
index 6178d57..f7d576e 100644
--- a/common/rfb/RREEncoder.h
+++ b/common/rfb/RREEncoder.h
@@ -25,11 +25,10 @@
 
   class RREEncoder : public Encoder {
   public:
-    static Encoder* create(SMsgWriter* writer);
-    virtual bool writeRect(const Rect& r, TransImageGetter* ig, Rect* actual);
-    virtual ~RREEncoder();
-  private:
     RREEncoder(SMsgWriter* writer);
+    virtual ~RREEncoder();
+    virtual bool writeRect(const Rect& r, TransImageGetter* ig, Rect* actual);
+  private:
     SMsgWriter* writer;
     rdr::MemOutStream mos;
   };