R1:73e88bb1010c

Point the Phabricator resource map back to webroot/, not webroot/rsrc/

Summary:
Ref T4222. Earlier, I adjusted the root from `webroot/` to `webroot/rsrc/`. However, this means that all the `/rsrc/x/y/z.jpg` fragments in CSS are no longer recognized as resource names.

Since we have like 9,000 things in CSS that do `url(/rsrc/xyz.jpg)` and I don't want to fix/test them all, so just make them work as-is. There's no real reason either setting is better than the other.

(Both URLs also work fine, but the…