Revert engage namespace sandbox for gpu on linux

Reason for revert: crashers.

TBR: piman@chromium.org
Bug: 789436
Change-Id: I34a72d3f528189099be6c67eb671809e052a1cb3
Reviewed-on: https://chromium-review.googlesource.com/801993
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520800}

content/gpu/gpu_sandbox_hook_linux.cc

@@ -342,9 +342,7 @@ bool GpuProcessPreSandboxHook(service_manager::BPFBasePolicy* policy,
   if (!LoadLibrariesForGpu(options))
     return false;
 
-  // TODO(tsepez): enable once we can proxy the stat(), readlink() syscalls.
-  if (!IsChromeOS() || !options.use_amd_specific_policies)
-    instance->EngageNamespaceSandbox(false /* from_zygote */);
+  // TODO(tsepez): enable namspace sandbox here once crashes are understood.
 
   errno = 0;
   return true;