Remove the channel weight from avgs_and_dirs calculation
Remove the channel weight from avgs_and_dirs calculation

Identical scaling was applied to all channels, and so could never
alter the direction of the returned partition direction vector, only
its magnitude. Later use normalizes the vector so this is redundant.

ARM-software/astc-encoder,ARM-software/astc-encoder,ARM-software/astc-encoder,ARM-software/astc-encoder