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>

cmd/tailscaled/install_darwin.go

@@ -123,7 +123,7 @@ func installSystemDaemonDarwin(args []string) (err error) {
 		return err
 	}
 
-	// Do not overwrite targetBin with the binary file if it it's already
+	// Do not overwrite targetBin with the binary file if it's already
 	// pointing to it. This is primarily to handle Homebrew that writes
 	// /usr/local/bin/tailscaled is a symlink to the actual binary.
 	if !same {