drm/amd/display: Remove unused tunnel BW validation

[Why & How]
The tunnel BW validation code has changed to the new one.
Remove the unused code.
The DP tunneling overhead is not updated in SST.
Move updating DP tunneling overhead for both SST and MST.

Reviewed-by: Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Signed-off-by: Cruise Hung <Cruise.Hung@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>