Fix the systemd wayland boot

Plasma-workspace currently starts kwin_wayland before afterwards
continuing to spawn the full session, through whatever mechanism.

We ultimately want to just have systemd manage everything all at once,
but this was not realised in time for 5.21 due to a problem of
propogating environment variables.

By removing this file we go to a working state with the option enabled,
and can build on it for the next release.

BUG: 432189


(cherry picked from commit ca81be66)