Fixes debian packaging checking wrong template.

debian/jitsi-meet-prosody.postinst

         . /usr/share/debconf/confmodule
 
         # detect dpkg-reconfigure, just delete old links
-        db_get jitsi-meet/jvb-hostname
+        db_get jitsi-meet-prosody/jvb-hostname
         JVB_HOSTNAME_OLD=$RET
         if [ -n "$RET" ] && [ ! "$JVB_HOSTNAME_OLD" = "$JVB_HOSTNAME" ] ; then
             rm -f /etc/prosody/conf.d/$JVB_HOSTNAME_OLD.cfg.lua