cleanup: remove unnecessary legacy interfaces (#656)

This diff addresses another point of https://github.com/ooni/probe/issues/1956:

> - [ ] observe that we're still using a bunch of private interfaces for common interfaces such as the `Dialer`, so we can get rid of these private interfaces and always use the ones in `model`, which allows us to remove a bunch of legacy wrappers

Additional cleanups may still be possible. The more I cleanup, the more I see
there's extra legacy code we can dispose of (which seems good?).

internal/engine/experiment/tlstool/internal/dialer.go

@@ -5,14 +5,14 @@ import (
 	"net"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 // Dialer creates net.Conn instances where (1) we delay writes if
 // a delay is configured and (2) we split outgoing buffers if there
 // is a configured splitter function.
 type Dialer struct {
-	netx.Dialer
+	model.Dialer
 	Delay    time.Duration
 	Splitter func([]byte) [][]byte
 }

internal/engine/experiment/tlstool/internal/fake_test.go

@@ -17,6 +17,8 @@ func (d FakeDialer) DialContext(ctx context.Context, network, address string) (n
 	return d.Conn, d.Err
 }
 
+func (d FakeDialer) CloseIdleConnections() {}
+
 type FakeConn struct {
 	ReadError             error
 	ReadData              []byte

internal/engine/experiment/tlstool/internal/internal.go

@@ -4,12 +4,12 @@ package internal
 import (
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 // DialerConfig contains the config for creating a dialer
 type DialerConfig struct {
-	Dialer netx.Dialer
+	Dialer model.Dialer
 	Delay  time.Duration
 	SNI    string
 }

internal/engine/experiment/tlstool/internal/internal_test.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/tlstool/internal"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 var config = internal.DialerConfig{
@@ -14,7 +15,7 @@ var config = internal.DialerConfig{
 	SNI:    "dns.google",
 }
 
-func dial(t *testing.T, d netx.Dialer) {
+func dial(t *testing.T, d model.Dialer) {
 	td := netx.NewTLSDialer(netx.Config{Dialer: d})
 	conn, err := td.DialTLSContext(context.Background(), "tcp", "dns.google:853")
 	if err != nil {

internal/engine/experiment/tlstool/tlstool.go

@@ -107,7 +107,7 @@ func (m Measurer) Run(
 	return nil // return nil so we always submit the measurement
 }
 
-func (m Measurer) newDialer(logger model.Logger) netx.Dialer {
+func (m Measurer) newDialer(logger model.Logger) model.Dialer {
 	// TODO(bassosimone): this is a resolver that should hopefully work
 	// in many places. Maybe allow to configure it?
 	resolver, err := netx.NewDNSClientWithOverrides(netx.Config{Logger: logger},