Revert "macV2GPUSandbox: Enable by default."

This reverts commit 5ba41218.

Reason for revert: The rollout on stable was reverted.

Original change's description:
> macV2GPUSandbox: Enable by default.
> 
> Enable the Mac V2 GPU Sandbox by default.
> 
> Bug: 917445
> Change-Id: I90c311663ab1a232d1669b86fef3f51d03fc1701
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2042287
> Auto-Submit: Greg Kerr <kerrnel@chromium.org>
> Commit-Queue: Avi Drissman <avi@chromium.org>
> Reviewed-by: Robert Sesek <rsesek@chromium.org>
> Reviewed-by: Avi Drissman <avi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#739466}

TBR=avi@chromium.org,kerrnel@chromium.org,rsesek@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 917445
Change-Id: I79e6e2ab0ac315ed1b84f8fd1aaf6fc320e258b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2065773Reviewed-by: Greg Kerr <kerrnel@chromium.org>
Auto-Submit: Greg Kerr <kerrnel@chromium.org>
Commit-Queue: Greg Kerr <kerrnel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742943}

content/public/common/content_features.cc

@@ -860,7 +860,7 @@ const base::Feature kMacSyscallSandbox{"MacSyscallSandbox",
                                        base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kMacV2GPUSandbox{"MacV2GPUSandbox",
-                                     base::FEATURE_ENABLED_BY_DEFAULT};
+                                     base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables retrying to obtain list of available cameras on Macbooks after
 // restarting the video capture service if a previous attempt delivered zero