从Golang文本文件中删除第一行

I'm trying to pop the first line of a file and thus reduce the file lines one by one. My implementation for removing the first line is as follows

type FS struct {
    ...
    File       *os.File
}

//File creation ok...


func (fs *Fs) pop() []byte {
    var buf []string
    scanner := bufio.NewScanner(fs.File)
    //Reading lines
    for scanner.Scan() {
        line := scanner.Text()
        buf = append(buf, line)
    }
    //Writing from second line on the same file
    for s := 1; s < len(buf); s++ {
        fs.File.WriteString(fmt.Println(buf[s]))
    }
    //Commit changes
    fs.File.Sync()
    fs.File.Close()

    return []byte(buf[0])
}

I get the returned []byte with the expected string but the file never changes. What am I missing here?