drm/i915/gvt: remove unused variable 'execlist'

Remove the variable 'execlist' as it's unused in function
vgpu_has_pending_workload.

Signed-off-by: Ping Gao <ping.a.gao@intel.com>
Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>