Fix chromium.webrtc win dimensions.

I made a mistake in my previous patch and actually removed dimensions
for chromium.webrtc.fyi. That's fine though, it made sense to do
anyway. Here is the correct fix.

Bug: 877018
Change-Id: Ia45c80a3c4bb2487198766e936c28f953c4a4e41
Reviewed-on: https://chromium-review.googlesource.com/c/1355182Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Patrik Höglund <phoglund@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612199}

infra/config/global/cr-buildbucket.cfg

@@ -3441,26 +3441,10 @@ buckets {
 
     # Win
 
-    builders {
-      mixins: "win"
-      name: "WebRTC Chromium Win Builder"
-      dimensions: "os:Windows-10"
-    }
-    builders {
-      mixins: "win"
-      name: "WebRTC Chromium Win10 Tester"
-      dimensions: "os:Windows-10"
-    }
-    builders {
-      mixins: "win"
-      name: "WebRTC Chromium Win7 Tester"
-      dimensions: "os:Windows-7"
-    }
-    builders {
-      mixins: "win"
-      name: "WebRTC Chromium Win8 Tester"
-      dimensions: "os:Windows-8.1"
-    }
+    builders { mixins: "win" name: "WebRTC Chromium Win Builder" }
+    builders { mixins: "win" name: "WebRTC Chromium Win10 Tester" }
+    builders { mixins: "win" name: "WebRTC Chromium Win7 Tester" }
+    builders { mixins: "win" name: "WebRTC Chromium Win8 Tester" }
   }
 }