Address `no-self-use` issues reported by pylint Sprinkle around `@staticmethod` where need be and raise `NotImplementedError` from `Entry.GetInitializer` instead of doing similar with `assert`. `NotImplementedError` will provide a hint to static analyzers that there are abstract methods which need to be implemented, if they aren't, in subclasses. Signed-off-by: Enji Cooper <yaneurabeya@gmail.com>