Fix thumbnail generation failure

o Change the impl of MediaMetadataRetriever.setDataSource(String).
  It opens and passes an fd to the media framework
  rather than pass the file path directly to the media server. The change is needed since media
  server does not have read permission to sdcard
o Remove the unnecessary jni method

Change-Id: I5a2f47dde804523d264b588f855ba2575a99c179