Extract auth components for Modular up to riot-web

[jryans]

The new auth design adds some UI elements that mention Modular to matrix-react-sdk. We should extract these Riot specific up to riot-web instead.

[kittykat]

@jryans could you confirm if this has been resolved? The only mention of Modular that I can find is in the changelog

[jryans]

Ah yes, the main component involved was the server type selector, and that was removed when we added the social login options, so there's no longer anything to do here.