drm/i915/gvt: Delete gvt_dbg_cmd() in cmd_parser_exec()

Since cmd message have been recorded in trace, gvt_dbg_cmd isn't
necessary. This will reduce much of dmesg as gvt_dbg_cmd is repeated
on each workload.

Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>