There's no destroyInstance in any LB* classes indeed. Seems to be caused by commit 1162ed5f88e5a77ea6feed971813914a95004b4f - looks like revert wasn't complete.

Ping @Catrope.

function itself seems to be removed here: https://github.com/wikimedia/mediawiki/commit/0e5cd18b74d83c50ebe7dd7ee9f09cf375aae9d7#diff-eda63d847b2ae3308eb4282b32562d42L159

(side note, diffusion doesn't show that removed method for some reason at https://phabricator.wikimedia.org/rMW0e5cd18b74d83c50ebe7dd7ee9f09cf375aae9d7#dd22b047 )

destroyInstance deleted in 0e5cd18b74d83c50ebe7dd7ee9f09cf375aae9d7

Change 315328 had a related patch set uploaded (by Smalyshev):
Call destroy method that actually exists instead of one that doesn't anymore.

https://gerrit.wikimedia.org/r/315328

Change 315332 had a related patch set uploaded (by Smalyshev):
Call destroy method that actually exists instead of one that doesn't anymore.

https://gerrit.wikimedia.org/r/315332

Change 315328 merged by jenkins-bot:
Call destroy method that actually exists instead of one that doesn't anymore.

https://gerrit.wikimedia.org/r/315328

Change 315332 merged by jenkins-bot:
Call destroy method that actually exists instead of one that doesn't anymore.

https://gerrit.wikimedia.org/r/315332

Mentioned in SAL (#wikimedia-operations) [2016-10-11T23:54:47Z] <ebernhardson@mira> Synchronized php-1.28.0-wmf.22/includes/ForkController.php: SWAT T147881 Call destroy method that actually exists instead of one that doesnt anymore. (duration: 00m 52s)