New cop: Lint/UselessMethodDefinition

[fatkodima]

There are at least 2 cases:

1. empty constructors - this may be just overriding parent's constructor, but this is bad anyway
2. methods just calling super

[ashmaroli]

I can think of one more use-case:

• private methods not used in any of the other instance methods of the Class. Modules shouldn't be affected by the cop since the method may have significance when the module is mixed-in somewhere.

[biinari]

For private methods not used within the class, what about a child class that uses a private method of its parent?

class Parent
  private

  def foo
    'something'
  end
end

class Child < Parent
  def bar
    foo
  end
end

I'm not sure I would make a strong case for not detecting that but I do have some code like this. It may at least be worth considering as an unsafe autocorrection.