slight adjustment to coef band definition

This commit adjusted slightly the 4x4 coefficents band definition to
better classify coefficients with similar distributions and usages.
It helps derf set about .1%, it is alos slightly positive for std-hd
set, where 4x4 blocks are used less frequently.

The commit also removed a const array not in use.

Change-Id: I78d16905d4036641ec905b0c32c190c1def5b249