R1:e6bfa1bd2388

Remove "mysql.configuration-provider" configuration option

Summary:
Ref T11044. This was old Facebook cruft for reading configuration from SMC (and maybe doing some other questionable things). See D183.

(See also D175 for discussion of this from 2011.)

In modern Phabricator, you can subclass `SiteConfig` to provide dynamic configuration, and we do so in the Phacility cluster. This lets you change any config, and change in response to requests (e.g., for instancing) and is generally more powerful than…