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/ZRLEEncoder.h b/common/rfb/ZRLEEncoder.h
index 61ff6fb..e3517c1 100644
--- a/common/rfb/ZRLEEncoder.h
+++ b/common/rfb/ZRLEEncoder.h
@@ -26,12 +26,10 @@
 
   class ZRLEEncoder : public Encoder {
   public:
-    static Encoder* create(SMsgWriter* writer);
-    virtual bool writeRect(const Rect& r, TransImageGetter* ig, Rect* actual);
-    virtual ~ZRLEEncoder();
-
-  private:
     ZRLEEncoder(SMsgWriter* writer);
+    virtual ~ZRLEEncoder();
+    virtual bool writeRect(const Rect& r, TransImageGetter* ig, Rect* actual);
+  private:
     SMsgWriter* writer;
     rdr::ZlibOutStream zos;
     rdr::MemOutStream mos;