drm/amd/display: Remove unused freesync functions

mod_freesync_get_vmin_vmax() and mod_freesync_get_v_position() were
added in 2017 by
commit 72ada5f7 ("drm/amd/display: FreeSync Auto Sweep Support")

mod_freesync_is_valid_range() was added in 2018 by
commit e80e9446 ("drm/amd/display: add method to check for supported
range")

mod_freesync_get_settings() was added in 2018 by
commit a3e1737e ("drm/amd/display: Implement stats logging")

and
mod_freesync_calc_field_rate_from_timing() was added in 2020 by
commit 49c70ece ("drm/amd/display: Change input parameter for
set_drr")

None of these have been used.

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>