drm/radeon/kms: remove useless radeon_ddc_dump()

The function didn't work with DP, eDP, or DP bridge
connectors and thus confused users as it lead them to
believe nothing was connected or the EDID was invalid
when in fact is was, just on the aux bus rather an i2c.

It should also speed up module loading as it avoids a
bunch of extra DDC probing.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>