drm/amd/display: Remove unused display_content_support

This was never filled in and thus never truly used.

Checking the EDID for content_type support is not required for sending
the avi infoframe packet.

v2:
- rebase to amd-staging-drm-next

Reviewed-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Joshua Ashton <joshua@froggi.es>
Signed-off-by: Melissa Wen <mwen@igalia.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>