all: Correct various typos

Skip-check: authors

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4005

cmd/syncthing/main.go

@@ -633,7 +633,7 @@ func syncthingMain(runtimeOptions RuntimeOptions) {
 	// report the error if there is one.
 	osutil.MaximizeOpenFileLimit()
 
-	// Ensure that that we have a certificate and key.
+	// Ensure that we have a certificate and key.
 	cert, err := tls.LoadX509KeyPair(locations[locCertFile], locations[locKeyFile])
 	if err != nil {
 		l.Infof("Generating ECDSA key and certificate for %s...", tlsDefaultCommonName)