lavc: drop libdirac encoder.

Libschroedinger is the preferred way to encode dirac video now, it
produces better output and has a nicer API.

libavcodec/allcodecs.c

@@ -371,7 +371,7 @@ void avcodec_register_all(void)
     REGISTER_ENCDEC  (XSUB, xsub);
 
     /* external libraries */
-    REGISTER_ENCDEC  (LIBDIRAC, libdirac);
+    REGISTER_DECODER (LIBDIRAC, libdirac);
     REGISTER_ENCODER (LIBFAAC, libfaac);
     REGISTER_ENCDEC  (LIBGSM, libgsm);
     REGISTER_ENCDEC  (LIBGSM_MS, libgsm_ms);