drm/i915/selftests: Remove unused local variable 'file'

drivers/gpu/drm/i915/gem/selftests/i915_gem_object_blt.c:453 igt_threaded_blt() error: uninitialized symbol 'file'.

Fixes: 34485832 ("drm/i915/selftests: Exercise parallel blit operations on a single ctx")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191112163643.3527-1-chris@chris-wilson.co.uk