Remove the unused valiable

[ikawaha]

Go version 1.10, go vet command strictly detects not used variables in tests as follows:

$ go vet ./app/test/
# cellar/app/test
app/test/bottle_testing.go:36:3: resp declared but not used

func ShowBottleNotFound(t goatest.TInterface, ctx context.Context, service *goa.Service, ctrl app.BottleController, bottleID interface{}) http.ResponseWriter {
        // Setup service
        var (
                logBuf bytes.Buffer
                resp   interface{} // ← ★

                respSetter goatest.ResponseSetterFunc = func(r interface{}) { resp = r }

This patch fix it to generate it only when the resp is used.

[raphael]

Great! thank you.

[raphael]

Can you please port that fix to the v1 branch as well? Thank you!