Revert "config: do not allow an ANY address as DNS recursor"

This reverts commit 1db8d3cb00.

agent/config/builder.go

@@ -726,11 +726,6 @@ func (b *Builder) Validate(rt RuntimeConfig) error {
 			return fmt.Errorf("DNS address cannot be a unix socket")
 		}
 	}
-	for _, a := range rt.DNSRecursors {
-		if ipaddr.IsAny(a) {
-			return fmt.Errorf("DNS recursor address cannot be 0.0.0.0, :: or [::]")
-		}
-	}
 	if rt.Bootstrap && !rt.ServerMode {
 		return fmt.Errorf("'bootstrap = true' requires 'server = true'")
 	}

agent/config/runtime_test.go

@@ -1463,15 +1463,6 @@ func TestConfigFlagsAndEdgecases(t *testing.T) {
 			hcl:  []string{`advertise_addr_wan = "::"`},
 			err:  "Advertise WAN address cannot be 0.0.0.0, :: or [::]",
 		},
-		{
-			desc: "recursors any",
-			flags: []string{
-				`-data-dir=` + dataDir,
-			},
-			json: []string{`{ "recursors": ["::"] }`},
-			hcl:  []string{`recursors = ["::"]`},
-			err:  "DNS recursor address cannot be 0.0.0.0, :: or [::]",
-		},
 		{
 			desc: "dns_config.udp_answer_limit invalid",
 			flags: []string{