Purge dict reading code for 401 and create for 402.

...android/inputmethod/latin/ExpandableBinaryDictionary.java

native/jni/NativeFileList.mk

.../src/suggest/policyimpl/dictionary/header/header_policy.h

.../policyimpl/dictionary/header/header_read_write_utils.cpp

.../policyimpl/dictionary/structure/backward/v402/Readme.txt

...tructure/backward/v402/bigram/ver4_bigram_list_policy.cpp

.../structure/backward/v402/bigram/ver4_bigram_list_policy.h

...y/structure/backward/v402/content/bigram_dict_content.cpp

...ary/structure/backward/v402/content/bigram_dict_content.h

...dictionary/structure/backward/v402/content/bigram_entry.h

...dictionary/structure/backward/v402/content/dict_content.h

...ucture/backward/v402/content/probability_dict_content.cpp

...tructure/backward/v402/content/probability_dict_content.h

...onary/structure/backward/v402/content/probability_entry.h

...structure/backward/v402/content/shortcut_dict_content.cpp

...y/structure/backward/v402/content/shortcut_dict_content.h

...ary/structure/backward/v402/content/single_dict_content.h

...cture/backward/v402/content/sparse_table_dict_content.cpp

...ructure/backward/v402/content/sparse_table_dict_content.h

.../backward/v402/content/terminal_position_lookup_table.cpp