Move duplicated functions (#33977)

Remove duplicated functions `IsExist`, `IsFile` and `IsDir` in package
`modules/git` and use the exists functions in `modules/util`.

modules/git/utils.go

@@ -8,7 +8,6 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io"
-	"os"
 	"strconv"
 	"strings"
 	"sync"
@@ -41,33 +40,6 @@ func (oc *ObjectCache[T]) Get(id string) (T, bool) {
 	return obj, has
 }
 
-// isDir returns true if given path is a directory,
-// or returns false when it's a file or does not exist.
-func isDir(dir string) bool {
-	f, e := os.Stat(dir)
-	if e != nil {
-		return false
-	}
-	return f.IsDir()
-}
-
-// isFile returns true if given path is a file,
-// or returns false when it's a directory or does not exist.
-func isFile(filePath string) bool {
-	f, e := os.Stat(filePath)
-	if e != nil {
-		return false
-	}
-	return !f.IsDir()
-}
-
-// isExist checks whether a file or directory exists.
-// It returns false when the file or directory does not exist.
-func isExist(path string) bool {
-	_, err := os.Stat(path)
-	return err == nil || os.IsExist(err)
-}
-
 // ConcatenateError concatenats an error with stderr string
 func ConcatenateError(err error, stderr string) error {
 	if len(stderr) == 0 {