Avoid mentioning hidden API in docs.

Change-Id: If83c179ec0d1b038e94a7fdca386c8ddf324e391

Author: jsharkey

core/java/android/os/Environment.java

@@ -518,9 +518,6 @@ public static File getExternalStorageAppCacheDirectory(String packageName) {
 
     /**
      * Gets the Android download/cache content directory.
-     * <p>
-     * Access to this path requires the
-     * {@link android.Manifest.permission#ACCESS_CACHE_FILESYSTEM} permission.
      */
     public static File getDownloadCacheDirectory() {
         return DOWNLOAD_CACHE_DIRECTORY;