refactor(netx): remove the self censorship mechanism (#364)

We're currently use jafar for QA and jafar is a better mechanism,
even though it is not portable outside of Linux.

This self censorship mechanism was less cool and added a bunch
of (also cognitive) complexity to netx.

If we ever want to go down a self censorship like road, we probably
want to do as little work as possible in the problem and as much
work as possible inside a helper like jafar.

Part of https://github.com/ooni/probe/issues/1591.

internal/engine/experiment/hhfm/hhfm.go

@@ -20,8 +20,8 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/dialer"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/errorx"
-	"github.com/ooni/probe-cli/v3/internal/engine/netx/selfcensor"
 	"github.com/ooni/probe-cli/v3/internal/randx"
 )
 
@@ -319,11 +319,11 @@ type Dialer struct {
 // DialContext dials a specific connection and arranges such that
 // headers in the outgoing request are transformed.
 func (d Dialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
-	dialer := d.Dialer
-	if dialer == nil {
-		dialer = selfcensor.DefaultDialer
+	child := d.Dialer
+	if child == nil {
+		child = dialer.Default
 	}
-	conn, err := dialer.DialContext(ctx, network, address)
+	conn, err := child.DialContext(ctx, network, address)
 	if err != nil {
 		return nil, err
 	}