Avoid autostarting kglobalaccel when shutting down

Order of our service teardown is somewhat undefined. kglobalaccel5 can
be closed before plasmashell.

On plasma exit we call setInactive/unregister on various kglobalaccel
actions and accidentally spawn kglobalaccel again.

If kglobalaccel is already closed, our actions aren't registered. There
is no point waking it up to try and remove an action. Use of the
setAutoStartService flag was chosen over checking if the kglobalaccel
service is still registered as that is still racey.

This was always slightly broken, but changes in the ecosystem means the
effect has worsened.

CCBUG: 429415