drm/amd/display: Remove additional FEC link bandwidth reduction

[why]
This is now done in the original link bandwidth calculation and DSC
must not do this anymore.

[how]
Remove the line of code that should have been removed when transition
to correctly applying FEC overhead was made.

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>