Remove dirac.c

Remove dirac.c

Comment says:
"NB, this is a temporary encoder only module until schroedinger
offers superior encoding quality than dirac-research"

http://diracvideo.org/2012/01/schroedinger-1-0-11/ says:
"Schrödinger outperforms dirac-research in most encoding situations,
both in terms of encoding speed and visual quality."