[INTERNAL] cleaned up AddXMPPAccountWizard

Removed dead method and unnecessary synchronization on UI thread
access.

Change-Id: Ie318fd1d3701b2c7d7c845ce7cbe435490ec59eb
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1913
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>