drm/amd/display: Drop unnecessary detect link code

Delete unnecessary codes in detect_link_and_local_sink. We already have
correct stop logic in dc_link_detect.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Ian Chen <ian.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>