Fix EZP-23171: dispatcher::delete() should accept arrays

> Fixes https://jira.ez.no/browse/EZP-23171

Calls `delete()` on each handler with the subset of filepath each handles.
It is not an assignation by reference, it is a logical operator (`&=`,  not `=&`). If any of the `delete()` calls returns `false`,  the final result will be `false`.