Remove log file fallback for non-TTY output

The feature that wrote logs to a file when stdout wasn't a terminal is
removed. Systemd services already handle log persistence through journald
and its logging facilities. This duplication is unnecessary and conflicts
with standard systemd logging practices.

View log in systemd:

```
journalctl -u rttys
```

or

```
journalctl -u rttys -f
```

Signed-off-by: Jianhui Zhao <zhaojh329@gmail.com>

log/log.go

@@ -1,51 +1,15 @@
 package log
 
 import (
-	"os"
 	"path/filepath"
-	"runtime"
 	"strconv"
-	"strings"
 
 	"github.com/dwdcth/consoleEx"
 	"github.com/mattn/go-colorable"
 	"github.com/rs/zerolog"
 	"github.com/rs/zerolog/log"
-	"golang.org/x/term"
 )
 
-type logFileHook struct {
-	err  error
-	path string
-}
-
-var logFile = &logFileHook{}
-
-func (h *logFileHook) Run(e *zerolog.Event, level zerolog.Level, msg string) {
-	if h.err != nil {
-		return
-	}
-
-	f, err := os.OpenFile(h.path, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
-	if err != nil {
-		h.err = err
-		log.Fatal().Msg(err.Error())
-		return
-	}
-	defer f.Close()
-
-	f.WriteString(zerolog.TimestampFunc().Format(zerolog.TimeFieldFormat) + " |")
-	f.WriteString(strings.ToUpper(level.String()) + "| ")
-
-	pc, file, line, ok := runtime.Caller(3)
-	if ok {
-		f.WriteString(zerolog.CallerMarshalFunc(pc, file, line) + " |")
-	}
-
-	f.WriteString(msg)
-	f.WriteString("\n")
-}
-
 func init() {
 	zerolog.CallerMarshalFunc = func(pc uintptr, file string, line int) string {
 		return filepath.Base(file) + ":" + strconv.Itoa(line)
@@ -54,20 +18,11 @@ func init() {
 	out := consoleEx.ConsoleWriterEx{Out: colorable.NewColorableStdout()}
 	logger := zerolog.New(out).With().Timestamp().Logger()
 
-	if !term.IsTerminal(int(os.Stdout.Fd())) {
-		logger = logger.Hook(logFile)
-	}
-
 	log.Logger = logger
 
 	zerolog.SetGlobalLevel(zerolog.InfoLevel)
 }
 
-// SetPath set the log file path
-func SetPath(path string) {
-	logFile.path = path
-}
-
 func Verbose() {
 	log.Logger = log.Logger.With().Caller().Logger()
 }