all: fix typos in comments

Fix its/it's, who's/whose, wether/whether, missing apostrophes
in contractions, and other misspellings across the codebase.

Updates #cleanup

Change-Id: I20453b81a7aceaa14ea2a551abba08a2e7f0a1d8
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/network-lock.go

@@ -407,7 +407,7 @@ func (b *LocalBackend) tkaSyncLocked(ourNodeKey key.NodePublic) error {
 	// has updates for us, or we have updates for the control plane.
 	//
 	// TODO(tom): Do we want to keep processing even if the Inform fails? Need
-	// to think through if theres holdback concerns here or not.
+	// to think through if there's holdback concerns here or not.
 	if len(offerResp.MissingAUMs) > 0 {
 		aums := make([]tka.AUM, len(offerResp.MissingAUMs))
 		for i, a := range offerResp.MissingAUMs {

ipn/ipnserver/server.go

@@ -429,7 +429,7 @@ func (s *Server) addActiveHTTPRequest(req *http.Request, actor ipnauth.Actor) (o
 	if len(s.activeReqs) == 1 {
 		if envknob.GOOS() == "windows" && !actor.IsLocalSystem() {
 			// Tell the LocalBackend about the identity we're now running as,
-			// unless its the SYSTEM user. That user is not a real account and
+			// unless it's the SYSTEM user. That user is not a real account and
 			// doesn't have a home directory.
 			lb.SetCurrentUser(actor)
 		}