infra: switch win10_chromium_x64_rel_ng to builderless.

Requires crrev.com/i/1714264

Bug: 994432
Change-Id: I81052b2cddbd4866f70b43993749e570d2a4756e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1773214Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690891}

infra/config/cr-buildbucket.cfg

@@ -879,6 +879,11 @@ builder_mixins {
   dimensions: "os:Windows"
 }
 
+builder_mixins {
+  name: "win10"
+  dimensions: "os:Windows-10"
+}
+
 builder_mixins {
   name: "win-angle-try"
   mixins: "win"
@@ -4753,8 +4758,11 @@ buckets {
     }
     builders { mixins: "win-try" name: "win10_chromium_x64_dbg_ng" }
     builders {
-      mixins: "win-try"
+      mixins: "builderless"
       mixins: "goma-j150"
+      mixins: "win-try"
+      mixins: "win10"
+      dimensions: "ssd:1"
       name: "win10_chromium_x64_rel_ng"
     }
     builders { mixins: "win-try" name: "win10_chromium_x64_rel_ng_exp" }