openat: remove unused function

The only user of this function was dropped in commit 90adf5c
("mkdir: do not return errors for incorrect directory modes or owners")
but we forgot to remove the function itself.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

openat_linux.go

@@ -42,10 +42,6 @@ func fstatatFile(dir *os.File, path string, flags int) (unix.Stat_t, error) {
 	return stat, nil
 }
 
-func fstatFile(fd *os.File) (unix.Stat_t, error) {
-	return fstatatFile(fd, "", unix.AT_EMPTY_PATH)
-}
-
 func readlinkatFile(dir *os.File, path string) (string, error) {
 	size := 4096
 	for {