Bug#767519: solr-jetty: update the path of dpkg-statoverride in the postrm script

[Emmanuel Bourg]

Package: solr-jetty
Version: 3.6.2+dfsg-4
Severity: serious

The postrm script of solr-jetty checks the existence of
/usr/sbin/dpkg-statoverride, but this path no longer exists since
dpkg/1.17.0. When solr-jetty is removed along jetty8 this brings dpkg in
a state where new installs fail because the statoverride file references
an unknown jetty user.