drm/amd/display: Remove check for DC_DMCUB_ENABLE on DCN42

drm/amd/display: Remove check for DC_DMCUB_ENABLE on DCN42

[why]
DCN without DMCUB is not a supported configuration on DCN42.

[how]
Remove the DC_DMCUB_ENABLE fuse register check and remove the
corresponding entries in the DCN42 DMUB register list.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Gabe Teeger <gabe.teeger@amd.com>
Signed-off-by: Matthew Stewart <Matthew.Stewart2@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Signed-off-by: Chuanyu Tseng <chuanyu.tseng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>