dashboard: remove issue for windows/arm builder

We originally left the issue attached to the builder, before we knew
that it worked. But it appears to be working well, with no shortage of
work to do from farmer.

Fixes golang/go#38607.

Change-Id: I0e654c825a92b64132efbc409b768e5e83967802
Reviewed-on: https://go-review.googlesource.com/c/build/+/273786
Trust: Jason A. Donenfeld <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: zx2c4

dashboard/builders.go

@@ -2204,9 +2204,8 @@ func init() {
 			"GO_TEST_TIMEOUT_SCALE=2"},
 	})
 	addBuilder(BuildConfig{
-		Name:       "windows-arm-zx2c4",
-		HostType:   "host-windows-arm64-zx2c4",
-		KnownIssue: 38607, // TODO: remove this after this builder has proved it works
+		Name:     "windows-arm-zx2c4",
+		HostType: "host-windows-arm64-zx2c4",
 		env: []string{
 			"GOARM=7",
 			"GO_TEST_TIMEOUT_SCALE=2"},