drm/amd/display: Remove unused definition of DMUB SET_CONFIG

[Why & How]
SET_CONFIG transactions with DMUB is not used and removed.

Signed-off-by: Meenakshikumar Somasundaram <[e-mail]>
Reviewed-by: Jun Lei <[e-mail]>
Acked-by: Stylon Wang <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h

···
 	 * Command type used for DP AUX Reply data notification
 	 */
 	DMUB_OUT_CMD__DP_AUX_REPLY = 1,
-	/**
-	 * Command type used for DP HPD event notification
-	 */
-	DMUB_OUT_CMD__DP_HPD_NOTIFY = 2,
 };
 
 #pragma pack(push, 1)