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/TightEncoder.h b/common/rfb/TightEncoder.h
index 465d8ed..5faef44 100644
--- a/common/rfb/TightEncoder.h
+++ b/common/rfb/TightEncoder.h
@@ -78,16 +78,16 @@
   
   class TightEncoder : public Encoder {
   public:
-    static Encoder* create(SMsgWriter* writer);
+    TightEncoder(SMsgWriter* writer);
+    virtual ~TightEncoder();
+
     virtual void setCompressLevel(int level);
     virtual void setQualityLevel(int level);
     virtual void setFineQualityLevel(int quality, JPEG_SUBSAMP subsampling);
     virtual int getNumRects(const Rect &r);
     virtual bool writeRect(const Rect& r, TransImageGetter* ig, Rect* actual);
-    virtual ~TightEncoder();
 
   private:
-    TightEncoder(SMsgWriter* writer);
     bool checkSolidTile(Rect& r, rdr::U32* colorPtr, bool needSameColor);
     void extendSolidArea(const Rect& r, rdr::U32 colorValue, Rect& er);
     void findBestSolidArea(Rect& r, rdr::U32 colorValue, Rect& bestr);