Remove PhabricatorStartup::getGlobal/setGlobal mechanism

Summary:
Ref T8424. Fixes T7114. This was envisioned as a per-request cache for reusing interpreters, but isn't a good fit for that in modern Phabricator.

In particular, it isn't loaded by the daemons, but they have equal need for per-request caching.

Since I finally need such a cache for Spaces, throw the old stuff away before I built a more modern cache.

Also resolves T7114 by dropping filtering on $_SERVER. I'm pretty sure this is the simplest fix, see D12977 for a bit more discussion.

Test Plan: Called didFatal() from somewhere in normal code and verified it was able to use the access log.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7114, T8424

Differential Revision: https://secure.phabricator.com/D13152