dashboard: revert Alpine GO_EXTLINK_ENABLED=1 change

See golang/go#19938 (comment)

Made things worse.

Updates golang/go#19938

Change-Id: I6c3e798c0b61ea5ee2c43af0aea5ee56e0f52032
Reviewed-on: https://go-review.googlesource.com/41812
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

dashboard/builders.go

@@ -795,9 +795,6 @@ func init() {
 	addBuilder(BuildConfig{
 		Name:     "linux-amd64-alpine",
 		HostType: "host-linux-x86-alpine",
-		env: []string{
-			"GO_EXTLINK_ENABLED=1", // Issue 18243 (internal linking broken)
-		},
 	})
 	// Add the -vetall builder. The builder name suffix "-vetall" is recognized by cmd/dist/test.go
 	// to only run the "go vet std cmd" test and no others.