drm/i915: Nuke pre-production GLK HDMI w/a 1139

w/a #1139 is only needed for pre-production GLK. Nuke it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200128155152.21977-1-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>