drm/i915: Eliminate skl_check_pipe_max_pixel_rate()

The normal cdclk handling now takes care of making sure the
plane's pixel rate doesn't exceed the spec appointed percentage
of the cdclk frequency. Thus we can nuke
skl_check_pipe_max_pixel_rate().

Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191015193035.25982-6-ville.syrjala@linux.intel.com