drm/i915: Remove unnecessary gen8_ppgtt_unmap_pages

We are already unmapping them in gen8_ppgtt_free. This function became
redundant since commit 06fda602dbca9c59d87db7da71192e4b54c9f5ff
("drm/i915: Create page table allocators").

Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/i915_gem_gtt.c
Simple merge