Remove obsolete low sample error propagate step.
Remove obsolete low sample error propagate step.

The codec has historically used a pass that uses a lower sample count's
error for a higher sample count during compute_angular_endpoints.
This is no longer beneficial, costing 2-3% performance and actually
reducing image quality.

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