Merge pull request #13582 from nextcloud/backport/13573/stable15

[stable15] Principals can be principal/user/<name> or principal/<name> from lega…

apps/dav/lib/Migration/RemoveClassifiedEventActivity.php

@@ -127,6 +127,6 @@ class RemoveClassifiedEventActivity implements IRepairStep {
 
 	protected function getPrincipal(string $principalUri): string {
 		$uri = explode('/', $principalUri);
-		return $uri[2];
+		return array_pop($uri);
 	}
 }