Remove duplicated directory "delete" on Linux

Inotify emits a IN_DELETE|IS_DIR event and a IN_DELETE_SELF event (in
this order) when a watched directory is removed, the former event
happens for all directories and generates a pair of a DirDeletedEvent
and a DirModifiedEvent instances, the latter used to generate a
(duplicated and unrequired) DirDeletedEvent

With this change, the test_fast_subdirectory_creation_deletion no
longer fails