ff_msmpeg4_decode_init() calls ff_h263_decode_init() which calls
MPV_common_init(), so calling both is redundant and leads to memory
leaks in WMV3/VC-1 decoder. Thus use only the first function in
WMV3/VC-1 decoder initialization.

Originally committed as revision 22024 to svn://svn.ffmpeg.org/ffmpeg/trunk
