all: fix typos where we repeat repeat ourselves

Found with the regex `\b([A-Za-z]+) \1\b`.

Updates #cleanup

Change-Id: I4cc51784d9b6437d3d0c66b531828707f87f7fd5
Signed-off-by: Alex Chan <alexc@tailscale.com>

ipn/ipnlocal/local.go

@@ -784,7 +784,7 @@ func (b *LocalBackend) onHomeDERPUpdate(du magicsock.HomeDERPChanged) {
 // In practice, it is possible that one profile with a homeDERP of 0 (no-derp)
 // got switched before setting any home DERP or that DERP IDs match across
 // DERP maps. Since the risk of this happening is small and the consequences
-// of this is is just a possible less optimal DERP until the next reSTUN,
+// of this is just a possible less optimal DERP until the next reSTUN,
 // accept this possibility.
 func (b *LocalBackend) onHomeDERPUpdateLocked(du magicsock.HomeDERPChanged) {
 	cn := b.currentNode()

ipn/ipnlocal/local_test.go

@@ -8301,7 +8301,7 @@ func TestDisplayMessageIPNBus(t *testing.T) {
 					if ok {
 						if diff := cmp.Diff(tt.wantWarning, got, cmpopts.IgnoreFields(health.UnhealthyState{}, "ETag")); diff != "" {
 							t.Errorf("unexpected warning details (-want/+got):\n%s", diff)
-							return true // we failed the test so tell the watcher we've seen what we need to to stop it waiting
+							return true // we failed the test so tell the watcher we've seen what we need to stop it waiting
 						}
 					} else {
 						got := slices.Collect(maps.Keys(n.Health.Warnings))