fix: unset systemd-user's DISPLAY env when system logs out

The DISPLAY environment variable should be reset
when logging out of the system to avoid the dde-session
using the wrong DISPLAY environment variable
in a multi-user login situation.

Log: as title
Pms: BUG-314781

Author: yixinshark

systemd/dde-session-manager.service.in

@@ -19,4 +19,5 @@ NotifyAccess=main
 ExecStart=@CMAKE_INSTALL_FULL_BINDIR@/dde-session --systemd-service
 ExecStopPost=@CMAKE_INSTALL_FULL_LIBEXECDIR@/dde-session-ctl --shutdown
 ExecStopPost=-/bin/sh -c 'test "$SERVICE_RESULT" != "exec-condition" && systemctl --user unset-environment XDG_CURRENT_DESKTOP'
+ExecStopPost=-/bin/sh -c 'test "$SERVICE_RESULT" != "exec-condition" && systemctl --user unset-environment DISPLAY'
 Slice=session.slice