reMarkable: Remove refresh before poweroff (#7563)

This is now handled in a platform-agnostic manner (#7558).

Co-authored-by: gbyl <gbyl@users.noreply.github.com>

frontend/device/remarkable/device.lua

@@ -190,8 +190,6 @@ function Remarkable:suspend()
 end
 
 function Remarkable:powerOff()
-    self.screen:clear()
-    self.screen:refreshFull()
     os.execute("systemctl poweroff")
 end