types/netmap: remove PrivateKey from NetworkMap

It's an unnecessary nuisance having it. We go out of our way to redact
it in so many places when we don't even need it there anyway.

Updates #12639

Change-Id: I5fc72e19e9cf36caeb42cf80ba430873f67167c3
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

types/key/util.go

@@ -10,9 +10,12 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"reflect"
 	"slices"
 
 	"go4.org/mem"
+	"tailscale.com/util/set"
+	"tailscale.com/util/testenv"
 )
 
 // rand fills b with cryptographically strong random bytes. Panics if
@@ -115,3 +118,18 @@ func debug32(k [32]byte) string {
 	dst[6] = ']'
 	return string(dst[:7])
 }
+
+// PrivateTypesForTest returns the set of private key types
+// in this package, for testing purposes.
+func PrivateTypesForTest() set.Set[reflect.Type] {
+	testenv.AssertInTest()
+	return set.Of(
+		reflect.TypeFor[ChallengePrivate](),
+		reflect.TypeFor[ControlPrivate](),
+		reflect.TypeFor[DiscoPrivate](),
+		reflect.TypeFor[MachinePrivate](),
+		reflect.TypeFor[NodePrivate](),
+		reflect.TypeFor[NLPrivate](),
+		reflect.TypeFor[HardwareAttestationKey](),
+	)
+}