drm/i915: Remove dead DKL_TX_LOADGEN_SHARING_PMD_DISABLE stuff

DKL_TX_LOADGEN_SHARING_PMD_DISABLE doesn't even seem to exist,
also the spec says to skip all loadgen stuff.

The code was dead anyway since it wasn't actually writing the value
anywhere.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211006204937.30774-6-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>