drm/amd/display: Drop CONFIG_DRM_AMD_DC_HDR

[Why & How]
Remove dead code.

Reviewed-by: Sun peng Li <Sunpeng.Li@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>