Update comments for win64_chromium_rel_ng in the CQ.

We plan to transition this to win10 bots on GCE, so I have
no plans to re-add this builder config to the CQ at this time.

TBR=tandrii@chromium.org
BUG=753184

Change-Id: Ia58f904c0d1c925ffb24f6ed6ba2122492a8f6c8
Reviewed-on: https://chromium-review.googlesource.com/716808
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508562}

infra/config/cq.cfg

@@ -93,8 +93,6 @@ verifiers {
         experiment_percentage: 100
       }
       builders { name: "win_chromium_compile_dbg_ng" }
-      # crbug.com/753184 - take out of the CQ temporarily.
-      # builders { name: "win_chromium_x64_rel_ng" }
       builders { name: "win_clang" }
       builders {
         name: "win10_chromium_x64_rel_ng"