Remove bigram dict content.

native/jni/NativeFileList.mk

...ictionary/structure/v4/bigram/ver4_bigram_list_policy.cpp

.../dictionary/structure/v4/bigram/ver4_bigram_list_policy.h

...l/dictionary/structure/v4/content/bigram_dict_content.cpp

...mpl/dictionary/structure/v4/content/bigram_dict_content.h

...policyimpl/dictionary/structure/v4/content/bigram_entry.h

.../policyimpl/dictionary/structure/v4/ver4_dict_buffers.cpp

...st/policyimpl/dictionary/structure/v4/ver4_dict_buffers.h

...olicyimpl/dictionary/structure/v4/ver4_dict_constants.cpp

.../policyimpl/dictionary/structure/v4/ver4_dict_constants.h

...ictionary/structure/v4/ver4_patricia_trie_node_writer.cpp

.../dictionary/structure/v4/ver4_patricia_trie_node_writer.h

...yimpl/dictionary/structure/v4/ver4_patricia_trie_policy.h

...ionary/structure/v4/ver4_patricia_trie_writing_helper.cpp

...ctionary/structure/v4/ver4_patricia_trie_writing_helper.h