drm/i915: Remove dummy i915_kick_out_firmware_fb

Since

commit 44adece5
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Aug 10 18:52:34 2016 +0200

    drm/fb-helper: Add a dummy remove_conflicting_framebuffers

the drm helpers take care of this for us.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161130110131.25668-1-daniel.vetter@ffwll.ch