Update status for CVE-2019-19343

While the issue is affecting both Undertow and remoting, cf.
https://bugzilla.redhat.com/show_bug.cgi?id=1780445#c10 on Red Hat's
side to mitigate the issue only a fix was added to remoting.

The CVE is quite specific for this memory leak in combination with
remoting, thus mark the severity as unimportant, beeing negligible for
Debian itself. Still, the issue remains unresolved for undertow, but it
does not appear to be interest in a fix.