Privatize a few constants in BinaryDictionary.java

java/src/com/android/inputmethod/latin/BinaryDictionary.java

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

...c/com/android/inputmethod/latin/ExpandableDictionary.java

java/src/com/android/inputmethod/latin/LastComposedWord.java

...rc/com/android/inputmethod/latin/RichInputConnection.java

.../com/android/inputmethod/latin/UserHistoryDictionary.java

java/src/com/android/inputmethod/latin/WordComposer.java