In article k7098v$a2c$1@ger.gmane.org, Tim Starling tstarling@wikimedia.org writes:
It's no longer necessary to remove LocalSettings.php to upgrade a wiki using the web installer. Just navigate to mw-config/index.php and follow the instructions.
I guess I'm a little confused on the terminology here; you said "upgrade a wiki", and as far as I know, I'm not upgrading my mediawiki to another version, just trying to run maintenance/update.php as per the installation instructions for an extension.