dashboard: remove known issue label from linux-arm-aws builder

The linux-arm-aws builder was initially labeled with a known issue
because it was experimental. The builder has been tested and is no
longer considered experimental.

Fixes golang/go#41867
Updates golang/go#40872
Updates golang/go#35628

Change-Id: I61f43f2c2651c26d3f5d4db01b779686ddb6a92b
Reviewed-on: https://go-review.googlesource.com/c/build/+/270517
Trust: Carlos Amedee <carlos@golang.org>
Run-TryBot: Carlos Amedee <carlos@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

dashboard/builders.go

@@ -2338,9 +2338,8 @@ func init() {
 		HostType: "host-linux-arm64-aws",
 	})
 	addBuilder(BuildConfig{
-		Name:       "linux-arm-aws",
-		HostType:   "host-linux-arm-aws",
-		KnownIssue: 41867, // builder being tested for reliability
+		Name:     "linux-arm-aws",
+		HostType: "host-linux-arm-aws",
 	})
 	addBuilder(BuildConfig{
 		FlakyNet:       true,