fix(signal): trim down tested endpoints (#1421)

## Checklist

- [x] I have read the [contribution
guidelines](https://github.com/ooni/probe-cli/blob/master/CONTRIBUTING.md)
- [x] reference issue for this pull request:
ooni/probe#2636
- [x] if you changed anything related to how experiments work and you
need to reflect these changes in the ooni/spec repository, please link
to the related ooni/spec pull request:
ooni/spec#282
- [x] if you changed code inside an experiment, make sure you bump its
version number

<!-- Reminder: Location of the issue tracker:
https://github.com/ooni/probe -->

## Description

This diff trims down the endpoints tested by signal to avoid the
possibility of future churn.

internal/experiment/signal/signal.go

@@ -15,7 +15,7 @@ import (
 
 const (
 	testName    = "signal"
-	testVersion = "0.2.4"
+	testVersion = "0.2.5"
 
 	signalCA = `-----BEGIN CERTIFICATE-----
 MIID7zCCAtegAwIBAgIJAIm6LatK5PNiMA0GCSqGSIb3DQEBBQUAMIGNMQswCQYD
@@ -162,25 +162,11 @@ func (m Measurer) Run(ctx context.Context, args *model.ExperimentArgs) error {
 		}
 	}
 
+	// See https://github.com/ooni/probe/issues/2636 for information
+	// about which of the many available targets we should test
 	inputs := []urlgetter.MultiInput{
-
 		// Here we need to provide the method explicitly. See
 		// https://github.com/ooni/probe-engine/issues/827.
-		{Target: "https://api.backup.signal.org/", Config: urlgetter.Config{
-			Method:          "GET",
-			FailOnHTTPError: false,
-			CertPool:        certPool,
-		}},
-		{Target: "https://cdn.signal.org/", Config: urlgetter.Config{
-			Method:          "GET",
-			FailOnHTTPError: false,
-			CertPool:        certPool,
-		}},
-		{Target: "https://cdn2.signal.org/", Config: urlgetter.Config{
-			Method:          "GET",
-			FailOnHTTPError: false,
-			CertPool:        certPool,
-		}},
 		{Target: "https://cdsi.signal.org/", Config: urlgetter.Config{
 			Method:          "GET",
 			FailOnHTTPError: false,
@@ -191,14 +177,6 @@ func (m Measurer) Run(ctx context.Context, args *model.ExperimentArgs) error {
 			FailOnHTTPError: false,
 			CertPool:        certPool,
 		}},
-		/*
-			TODO: understand why this endpoint does not speak TLS
-			{Target: "https://contentproxy.signal.org/", Config: urlgetter.Config{
-				Method:          "GET",
-				FailOnHTTPError: false,
-				CertPool:        certPool,
-			}},
-		*/
 		{Target: "https://sfu.voip.signal.org/", Config: urlgetter.Config{
 			Method:          "GET",
 			FailOnHTTPError: false,
@@ -209,26 +187,6 @@ func (m Measurer) Run(ctx context.Context, args *model.ExperimentArgs) error {
 			FailOnHTTPError: false,
 			CertPool:        certPool,
 		}},
-		{Target: "https://svr2.signal.org/", Config: urlgetter.Config{
-			Method:          "GET",
-			FailOnHTTPError: false,
-			CertPool:        certPool,
-		}},
-		{Target: "https://ud-chat.signal.org/", Config: urlgetter.Config{
-			Method:          "GET",
-			FailOnHTTPError: false,
-			CertPool:        certPool,
-		}},
-		{Target: "https://updates.signal.org/", Config: urlgetter.Config{
-			Method:          "GET",
-			FailOnHTTPError: false,
-			CertPool:        certPool,
-		}},
-		{Target: "https://updates2.signal.org/", Config: urlgetter.Config{
-			Method:          "GET",
-			FailOnHTTPError: false,
-			CertPool:        certPool,
-		}},
 		{Target: "dnslookup://uptime.signal.org"},
 	}
 	multi := urlgetter.Multi{Begin: time.Now(), Getter: m.Getter, Session: sess}

internal/experiment/signal/signal_test.go

@@ -17,7 +17,7 @@ func TestNewExperimentMeasurer(t *testing.T) {
 	if measurer.ExperimentName() != "signal" {
 		t.Fatal("unexpected name")
 	}
-	if measurer.ExperimentVersion() != "0.2.4" {
+	if measurer.ExperimentVersion() != "0.2.5" {
 		t.Fatal("unexpected version")
 	}
 }