Revert "drm/i915: Implement Link Rate fallback on Link training failure"

This reverts commit 233ce881

.

I assumed it's ok, but really should have double-checked - CI caught
tons of fail :(

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Acked-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170301171749.13053-1-daniel.vetter@ffwll.ch