Rename the dependees goal to dependents.

[benjyw]

Also fix various casual uses of the term dependees in comments and docs.

[Eric-Arellano]

For posterity, it would be helpful to give a tldr of the Slack discussion of why this change was made.

[benjyw]

if a.py imports from b.py, it turns out that b is the "dependee" (see e.g., https://en.wiktionary.org/wiki/dependee#:~:text=dependee%20(plural%20dependees),used%20in%20agent%2Doriented%20programming)) but we were using that term to describe a.py. So we were using the term incorrectly.