Since RDO doesn't care about what order bit costs are calculated, merge sigmap and level coding into the same loop in RDO.
This is bit-exact for 4x4dct but slightly incorrect for 8x8dct due to the sigmap containing duplicated contexts.
However, the PSNR penalty of this is extremely small (~0.001db).
Speed benefit is about 15% in 4x4dct and 30% in 8x8dct residual bit cost calculation at QP20.
Overall encoding speed benefit is up to 5%, depending on encoding settings.
Also remove an old unnecessary CABAC table that hasn't been used for years.