macOS V2 Sandbox: Disable V2 for GPU sandbox.

This CL reverts the GPU process to the V1 sandbox while a series of
hangs are resolved.

Tbr: creis@chromium.org
Bug: 812228
Change-Id: Ie87cf5228d19cf3c50892b2f19133c3d3f2e2593
Reviewed-on: https://chromium-review.googlesource.com/957463
Commit-Queue: Greg Kerr <kerrnel@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542232}

content/browser/child_process_launcher_helper_mac.cc

@@ -82,7 +82,6 @@ bool ChildProcessLauncherHelper::BeforeLaunchOnLauncherThread(
     case service_manager::SANDBOX_TYPE_NACL_LOADER:
     case service_manager::SANDBOX_TYPE_PDF_COMPOSITOR:
     case service_manager::SANDBOX_TYPE_PROFILING:
-    case service_manager::SANDBOX_TYPE_GPU:
       v2_process = true;
       break;
     default: