Don't require a DB connection to run the i18n string extractor
Summary: Part of T16378. I remember this being a pain when I first tried to set up the WMF translations extension.
Test Plan: Bork your db config somehow. Run `./bin/i18n`. See it doesn't fail (it may spit out a warning though)
Reviewers: O1 Blessed Committers, mainframe98
Reviewed By: O1 Blessed Committers, mainframe98
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D26562