Move ksmserver's ksplash notifying to ksmserver
Previously the call to ksplash was being emitted by plasma-session. This isn't used in the systemd startup so it was introduced in a somewhat messy script.
This script has an issue:
If ksplash is disabled the bus name won't be registered. Typically this isn't an issue. However to avoid a race condition ksplash registers itself as being DBus activatable, so that the dbus server holds dispatching the message.
This combo means ksmserver our unit is considered as not running until our script times out. This then defers other things in the chain that depend on ksmserver.
Moving the call into the relevant piece of code into ksmserver unifies things into a single path and gives us more control.