[ozone] Remove unneeded workaround for disabling display controllers.

ui/ozone/platform/drm/gpu/screen_manager.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/ozone/platform/drm/gpu/screen_manager.h"
 
 #include <xf86drmMode.h>
 
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "ui/gfx/geometry/point.h"
@@ skipping 164 matching lines @@
     uint32_t crtc) {
   HardwareDisplayControllers::iterator it = FindDisplayController(drm, crtc);
   if (it != controllers_.end()) {
     HardwareDisplayController* controller = *it;
     if (controller->IsMirrored()) {
       controller = new HardwareDisplayController(
           controller->RemoveCrtc(drm, crtc), controller->origin());
       controllers_.push_back(controller);
     }
 
-    if (!controller->IsDisabled()) {
-      // Workaround for driver bug that does not release the buffer on null
-      // modeset.
-      ModesetDisplayController(controller, controller->origin(),
-                               controller->get_mode(), false);
-    }
-
     controller->Disable();
     UpdateControllerToWindowMapping();
     return true;
   }
 
   LOG(ERROR) << "Failed to find display controller crtc=" << crtc;
   return false;
 }
 
 HardwareDisplayController* ScreenManager::GetDisplayController(
@@ skipping 153 matching lines @@
 DrmWindow* ScreenManager::FindWindowAt(const gfx::Rect& bounds) const {
   for (auto pair : window_map_) {
     if (pair.second->bounds() == bounds)
       return pair.second;
   }
 
   return nullptr;
 }
 
 }  // namespace ui