dct/rdft: Remove duplicate typedefs for context structs

The typedefs also exist in the avfft.h header and since typedefs cannot be
legally redefined in C, the code fails to compile with some compilers.

This reverts commits 11c7155cce and 57f1b1dcc7.
qpeldsp: Mark source pointer in qpel_mc_func function pointer const
vc1dsp: Add wrappers for {avg|put}_vc1_mspel_mc00_c

This avoids invoking the wrapped functions with too many arguments.
fft-test: Pass the right struct members instead of casting
mpegvideo: Drop unused MPEG_BUF_SIZE and CHROMA_444 defines
mpegvideo: Move ME_MAP_* defines to the only place they are used
mpegvideo: Move QMAT_SHIFT* defines to the only place they are used