drm/i915: Remove duplicate header from i915_request.h

Remove i915_scheduler.h which is included more than once

Signed-off-by: Brajeswar Ghosh <brajeswar.linux@gmail.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20181225132340.GA2584@hp-pavilion-15-notebook-pc-brajeswar