mw.libs.ve.unsupportedList (formerly named "blacklist") still lists opera: [ [ '<', 12 ] ], but according to https://www.mediawiki.org/wiki/Compatibility#Browser_support_matrix Opera < 15 won't receive any JS at all, so this is no longer necessary. The list is specified via VisualEditorBrowserUnsupportedList in extension.json and exposed to the client's JavaScript via wgVisualEditorConfig.

(I actually don't see whether https://phabricator.wikimedia.org/source/mediawiki/browse/master/resources/src/startup/startup.js really blocks all Opera versions below 15, but the test for strict mode does block at least all versions below 12.1.)