Remove or correct various "phabricator/" references to "libphutil"

Summary:
Ref T13395. "libphutil/" was stripped for parts, but some documentation still references it. This is mostly minor corrections, but:

• Removes "Javelin at Facebook", long obsolete.
• Removes "php FPM warmup", which was always a prototype and is obsoleted by PHP preloading in recent PHP.

Test Plan: grep / reading

Maniphest Tasks: T13395

Differential Revision: https://secure.phabricator.com/D21624