drm/i915: Remove incorrect warning in context cleanup

Commit e9f24d5f
Author: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Date:   Mon Oct 5 13:26:36 2015 +0100

    drm/i915: Clean up associated VMAs on context destruction

Added a warning based on an incorrect assumption that all VMAs
in a VM will be on the inactive list at the point last reference
to a context and VM is dropped.

This is not true because i915_gem_object_retire__read will not
put VMA on the inactive list until all activities on the object
in question (in all VMs) have been retired.

As a consequence, whether or not a context/VM will be destroyed
with its VMAs still on the active list, can depend on completely
unrelated activities using the same object from a different
context or engine.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92638
Testcase: igt/gem_request_retire/retire-vma-not-inactive
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michel Thierry <michel.thierry@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448025816-25584-1-git-send-email-tvrtko.ursulin@linux.intel.comSigned-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_context.c

@@ -141,8 +141,6 @@ static void i915_gem_context_clean(struct intel_context *ctx)
 	if (!ppgtt)
 		return;
 
-	WARN_ON(!list_empty(&ppgtt->base.active_list));
-
 	list_for_each_entry_safe(vma, next, &ppgtt->base.inactive_list,
 				 mm_list) {
 		if (WARN_ON(__i915_vma_unbind_no_wait(vma)))