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

Updates #8419

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

types/logid/id.go

@@ -11,9 +11,8 @@ import (
 	"encoding/binary"
 	"encoding/hex"
 	"fmt"
+	"slices"
 	"unicode/utf8"
-
-	"golang.org/x/exp/slices"
 )
 
 // PrivateID represents a log steam for writing.

types/views/views.go

@@ -8,10 +8,10 @@ package views
 import (
 	"encoding/json"
 	"errors"
+	"maps"
 	"net/netip"
+	"slices"
 
-	"golang.org/x/exp/maps"
-	"golang.org/x/exp/slices"
 	"tailscale.com/net/tsaddr"
 )