Remove rc_scratch references

[jreiland]

Address issue #383

[b-reyes]

I think all of your changes look good. One thing I think we should change is that on the filesystems.md page there are references to scratch. It was previously written this way because there were separate scratch directories for Alpine and Blanca. I think we should change all of these references to /scratch/alpine. For example, here is an occurrence of this:

I think this will hopefully reduce any confusion. Although I am sure people will still be confused that is says "alpine". If you think it is appropriate, you can turn the important admonition into a bullet list and the second bullet (or first) you can explain that Alpine and Blanca now share the same scratch directory and it is called /scratch/alpine.

[b-reyes]

I think this looks good! I made one small suggestion on a comma that I think should be removed. If you don't think it should be removed, no worries you can resolve that conversation.