Reduce context model number from 9 to 6.
Let context be two kinds: two reference frames are equal distance
or not.
Also, give equal distance compound weight {9, 7} instead of {8, 8}/16

Reducing context model gives neutral performance.
New compound weight provides -0.14% gain.

Change-Id: I8a3f3021eac9e446ac826e5992f42931af4c8962