Remove BrightId sponsorship from the front end

[yuetloo]

This PR removes the BrightId sponsorship logic in the frontend and the deployment script.

Todo's for next major release:

1. Remove the BrightIdSponsor contract
2. Update the BrightIdUserRegistry contract to remove references to the BrightIdSponsor contract.

See issue #749

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[auryn-macmillan]

lgtm