drm/amdgpu: Remove drm_fb_helper_{add,remove}_one_connector calls

drm_fb_helper_{add,remove}_one_connector() are dummy functions now
and serve no purpose. Hence remove their calls.

This is the preparatory step for removing the
drm_fb_helper_{add,remove}_one_connector() functions from
drm_fb_helper.h

Signed-off-by: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200305120434.111091-4-pankaj.laxminarayan.bharadiya@intel.com