Lint/UselessAccessModifier doesn't recognize conditionally defined methods

[bquorning]

When a class or module uses if to conditionally define a private method, the Lint/UselessAccessModifier cop seems to thing that the private access modifier is useless.

Expected behavior

No offenses.

Actual behavior

One offense:

test.rb:8:3: W: Useless private access modifier.
  private
  ^^^^^^^

Steps to reproduce the problem

Run rubocop on this (contrived) test.rb file:

# encoding: utf-8
# frozen_string_literal: true
class Foo
  def initialize
    puts value
  end

  private

  if defined?(Bar)
    def value
      true
    end
  else
    def value
      false
    end
  end
end

RuboCop version

» bin/rubocop -V
0.39.0 (using Parser 2.3.0.7, running on ruby 2.3.0 x86_64-darwin15)
» git log -1 --pretty=format:'%H'
3564db025d475397ab2a0ebb9d584a114421c198