remove obsolete comment about page maps

(cherry picked from commit bea11510645192d94b6b2c226e220b72a1364d15)
WICKET-5642 CheckingOutputObjectStream should filter duplicates by identity, not by equality

(cherry picked from commit e8e184b289a595b96d1090a6e94a97c72aa946af)
WICKET-5639 ResourceResponse does not write headers when status code is set

(cherry picked from commit c95d8f74c30a1838daa9c92208bcbe8904372957)