Update SDR outputs (and other SDR details if needed)

[emilyanndavis]

A user on the forum pointed out that they couldn't find weighted_avg_aspect.tif in SDR's intermediate outputs.

After digging through the commit history, I discovered that weighted_avg_aspect.tif was removed in InVEST 3.14.0 when there was a major update to the SDR LS factor.

In addition to removing weighted_avg_aspect.tif from the list of outputs, we should make sure the User Guide isn't missing any more significant updates to the SDR discussion.

[dcdenu4]

Another good reminder that we might want to prioritize linking the InVEST model output spec to the User Guide, as we do the args spec.