Dispatching was prevented for disconnected client errors after
recent reports like #32042 when running on Tomcat, and the
async request was completed from the onError notification.
This has the side effect of not allowing exception resolvers
to take final action even if the response is not writeable.
After all updates for this issue, it appears the dispatch no
longer causes issues. Tomcat actually does not do the dispatch,
but it doesn't seem to cause any issues, and on other servers
like Jetty where the dispatch works, applications can have a
chance to handle the exception.
This change removes the disconnected client checks and allows
dispatching again. After the change DisconnectedClientHelper
is no longer needed in the 5.3.x branch.
See gh-32342
dd5fe68522