vlc_opendir: simplify and partly revert previous commit

opendir() sets close-on-exec anyway.

src/posix/filesystem.c

@@ -133,18 +133,7 @@ int vlc_mkdir (const char *dirname, mode_t mode)
  */
 DIR *vlc_opendir (const char *dirname)
 {
-#ifdef O_DIRECTORY
-    int fd = vlc_open (dirname, O_RDONLY | O_DIRECTORY);
-#else /* If O_DIRECTORY is missing. fdopendir() will deal with ENOTDIR. */
-    int fd = vlc_open (dirname, O_RDONLY);
-#endif
-    if (fd == -1)
-        return NULL;
-
-    DIR *dir = fdopendir (fd);
-    if (dir == NULL)
-        close (fd);
-    return dir;
+    return opendir (dirname);
 }
 
 /**