remove deprecated libwebm functions

WriteMetadataBlock and WriteSimpleBlock were removed in libwebm:
commit b6311dc16f0c1a0d7b31ac44a44fd96ce7505727
Author: Vignesh Venkatasubramanian <vigneshv@google.com>
Date:   Thu May 7 13:58:33 2015 -0700

    mkvmuxer: Refactor to remove a lot of duplicate code

BUG=webm:1480
1 file changed
tree: 89688efd7096caf0b86ecaed8407c501e4cc3ae3
  1. JNI/