amdgpu sandbox: Don't forcibly load swrast_dri.so.

This library shouldn't be needed, and after some build changes on the
Chrome OS side, is no longer present.

BUG=b:67860772
TEST=deploy_chrome, confirmed browser works fine.

Change-Id: Id0be85f5f36da6435dcc605a2b73a7c5ac095e16
Reviewed-on: https://chromium-review.googlesource.com/722109Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Commit-Queue: Justin TerAvest <teravest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509627}

content/common/sandbox_init_gpu_linux.cc

@@ -362,10 +362,6 @@ bool CrosAmdGpuPreSandboxHook(GpuProcessPolicy* policy) {
     LOG(ERROR) << "dlopen(libglapi.so) failed with error: " << dlerror();
     return false;
   }
-  if (NULL == dlopen("/usr/lib64/dri/swrast_dri.so", dlopen_flag)) {
-    LOG(ERROR) << "dlopen(swrast_dri.so) failed with error: " << dlerror();
-    return false;
-  }
   if (NULL == dlopen("/usr/lib64/dri/radeonsi_dri.so", dlopen_flag)) {
     LOG(ERROR) << "dlopen(radeonsi_dri.so) failed with error: " << dlerror();
     return false;