drm/xe: Fix xe_gt_throttle_sysfs.h

We don't need to include drm/drm_managed.h here.
We don't need to comment final #endif.
Also remove empty line at the end.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240513084218.2084-2-michal.wajdeczko@intel.com