Revert "Turn on presentation feedback for Linux"

This reverts commit 66531351.

Reason for revert: broke webgl_conformance_gl_passthrough_tests on all Linux bots; see https://bugs.chromium.org/p/chromium/issues/detail?id=776877#c31 .

Original change's description:
> Turn on presentation feedback for Linux
> 
> Bug: 776877
> Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
> Change-Id: I9d9590a5174db94392a447ab280e9218b37c2958
> Reviewed-on: https://chromium-review.googlesource.com/1040725
> Reviewed-by: Antoine Labour <piman@chromium.org>
> Commit-Queue: Peng Huang <penghuang@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#555782}

TBR=penghuang@chromium.org,piman@chromium.org

Change-Id: Ib7da20d9bfb7729a6afadf075c7b99a58131014a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 776877
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Reviewed-on: https://chromium-review.googlesource.com/1043227Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555927}

ui/gl/gl_switches_util.cc

@@ -13,7 +13,7 @@ namespace gl {
 
 bool IsPresentationCallbackEnabled() {
 // TODO(peng): always enable once 776877 is fixed.
-#if defined(OS_CHROMEOS) || defined(OS_ANDROID) || defined(OS_LINUX)
+#if defined(OS_CHROMEOS) || defined(OS_ANDROID)
   return true;
 #else
   return base::CommandLine::ForCurrentProcess()->HasSwitch(