drm/amd/display: Destroy aux_engines only once

[Why]
In the dce112 function to destroy the resource pool, engines
(the aux engines) is destroyed twice.  This has no ill effects
but is a tad redundant.

[How]
Remove the redundant call

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>