Revert "[infra] Temporarily disable Windows SDK builder on CQ"

This reverts commit 7594c15.

Reason for revert: https://crbug.com/830533 has been fixed and the
windows bots are back again.

Original change's description:
> [infra] Temporarily disable Windows SDK builder on CQ
> 
> [email protected]
> 
> Change-Id: I348d14b021fc7fc859dec39e88de4e3876385c7a
> Reviewed-on: https://dart-review.googlesource.com/50180
> Reviewed-by: Alexander Thomas <[email protected]>

[email protected],[email protected]

Change-Id: I50c24d65a96f8f45b0ee2b821176a00c61998590
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/50241
Reviewed-by: Alexander Thomas <[email protected]>
Commit-Queue: Alexander Thomas <[email protected]>

Author: athomas

tools/infra/config/cq.cfg

@@ -30,6 +30,7 @@ verifiers {
       builders { name: "pkg-linux-release-try"}
       builders { name: "ddc-linux-release-chrome-try"}
       builders { name: "vm-linux-product-x64-try"}
+      builders { name: "dart-sdk-windows-try"}
       builders { name: "vm-kernel-legacy-linux-release-x64-try"}
       builders { name: "vm-kernel-mac-release-x64-try"}
       builders { name: "benchmark-linux-try"}