drm/i915: Remove unused/wrong INF_UNIT_LEVEL_CLKGATE

INF_UNIT_LEVEL_CLKGATE is not replicated, but since it's not actually
used it can just be removed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230206165410.3056073-2-lucas.demarchi@intel.com