Revert "drm/amd/display: Don't skip link training for empty dongle"

This reverts commit 80adaebd2d411b7d6872a097634848a71eb13d20.

[WHY]
This change was working around a regression that occured in this:
commit 0301ccbaf67d ("drm/amd/display: DP Compliance 400.1.1 failure")

With the fix to run verify_link_cap when the SINK_COUNT of
dongles becomes non-zero this change is no longer needed.

Cc: Louis Li <[e-mail]>
Cc: Wenjing Liu <[e-mail]>
Cc: Hersen Wu <[e-mail]>
Cc: Eric Yang <[e-mail]>
Reviewed-by: Wenjing Liu <[e-mail]>
Signed-off-by: Harry Wentland <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/core/dc_link.c

···
 				if (memcmp(&link->dpcd_caps, &prev_dpcd_caps, sizeof(struct dpcd_caps)))
 					same_dpcd = false;
 			}
-			/* Active dongle plug in without display or downstream unplug*/
+			/* Active dongle downstream unplug*/
 			if (link->type == dc_connection_active_dongle &&
 				link->dpcd_caps.sink_count.bits.SINK_COUNT == 0) {
-				if (prev_sink != NULL) {
+				if (prev_sink != NULL)
 					/* Downstream unplug */
 					dc_sink_release(prev_sink);
-				} else {
-					/* Empty dongle plug in */
-					dp_verify_link_cap_with_retries(link,
-							&link->reported_link_cap,
-							LINK_TRAINING_MAX_VERIFY_RETRY);
-				}
 				return true;
 			}