Fix crash in vault listing callback

DBus::asyncCall did not auto disconnect when our applet gets deleted. If
plasma gets reset during such an operation we would end up crashing.

There's no need to have wrappers used by one applet. It just adds
maintenence burden on everyone else.

This patch replaces the wrapper with calls that don't require string
based arguments which is better long term. This also highlighted
that the XML file we were using was out of date.