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

This reverts commit 80adaebd.

[WHY]
This change was working around a regression that occured in this:
commit 0301ccba ("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 <Ching-shih.Li@amd.com>
Cc: Wenjing Liu <Wenjing.Liu@amd.com>
Cc: Hersen Wu <hersenxs.wu@amd.com>
Cc: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>