drm/i915/debugfs: Do not report currently active engine when describing objects

It is not very useful to have code which tries to report a rapidly
transient state which will not report anything majority of the time,
especially since it is currently only used from
<debugfs>/i915_gem_framebuffers.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Acked-by: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210915114153.951670-1-tvrtko.ursulin@linux.intel.com