[DOC] Remove VoIP and ScreenSharing from architecture image

VoIP and Screensharing were removed:
* https://github.com/saros-project/saros/commit/8c8e70d
* https://github.com/saros-project/saros/commit/55f4358

This patch continues their removal in the architecture images.

Change-Id: I8676e34acc2f63d092ffdf1062c7fdef80e0f996
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1464
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>
Tested-by: Franz Zieris <zieris@inf.fu-berlin.de>