Expose multi-CV feature downstream

[jeremylenz]

This removes allow_multiple_content_views from UpstreamOnlySettings, allowing it to be exposed downstream.

I didn't remove the UpstreamOnlySettings feature entirely, because I thought it might be handy to have in the future? thoughts welcome.

[evgeni]

Stubbing constants is weird (in Ruby?). You'd need stub_const from either rspec-mocks or minitest-stub-const for that, I think.

[jeremylenz]

Originally I was just setting them in the test, but that felt weird too. What's the non-weird way?

[ShimShtein]

I think it would be better to redesign the UpstreamOnlySettings module to be a proper class:

class UpstreamOnlySettings
  def self.include?(key)
    new.include?
  def include?(key)
    SETTINGS.include?(key.to_s)
  end
end

Then it would be easier to stub the class:

UpstreamOnlySettings.any_instance.stubs(:include?).returns(false)

[jeremylenz]

@ShimShtein good idea! updated.

I'm relying on CI to see if my tests are good, looks like someone needs to click a button for me