all: fix more typos caused by unnecessary repetition

Updates #cleanup

Change-Id: I5c0b8f0152581231252ab97dd1820d8b3fcbe450
Signed-off-by: Alex Chan <alexc@tailscale.com>

types/key/machine.go

@@ -167,7 +167,7 @@ func (k MachinePrivate) OpenFrom(p MachinePublic, ciphertext []byte) (cleartext
 	return box.Open(nil, ciphertext[len(nonce):], &nonce, &p.k, &k.k)
 }
 
-// MachinePublic is the public portion of a a MachinePrivate.
+// MachinePublic is the public portion of a MachinePrivate.
 type MachinePublic struct {
 	k [32]byte
 }

types/key/nl.go

@@ -111,7 +111,7 @@ func (k NLPrivate) SignNKS(sigHash tkatype.NKSSigHash) ([]byte, error) {
 	return ed25519.Sign(ed25519.PrivateKey(k.k[:]), sigHash[:]), nil
 }
 
-// NLPublic is the public portion of a a NLPrivate.
+// NLPublic is the public portion of a NLPrivate.
 type NLPublic struct {
 	k [ed25519.PublicKeySize]byte
 }