all: use Go 1.21 slices, maps instead of x/exp/{slices,maps}

Updates #8419

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/filter/filter.go

@@ -7,11 +7,11 @@ package filter
 import (
 	"fmt"
 	"net/netip"
+	"slices"
 	"sync"
 	"time"
 
 	"go4.org/netipx"
-	"golang.org/x/exp/slices"
 	"tailscale.com/envknob"
 	"tailscale.com/net/flowtrack"
 	"tailscale.com/net/netaddr"

wgengine/filter/filter_test.go

@@ -7,6 +7,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"net/netip"
+	"slices"
 	"strconv"
 	"strings"
 	"testing"
@@ -14,7 +15,6 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"go4.org/netipx"
 	"golang.org/x/exp/maps"
-	"golang.org/x/exp/slices"
 	"tailscale.com/net/packet"
 	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"