Remove title and icon fields

[connor-moody]

This whatwg/HTML PR proposes simplifying registerProtocolHandler() by removing the title argument. To ensure that declarative protocol_handlers in PWA manifests and the registerProtocolHandlers() API are as aligned as closely as possible, the title field and the related icon field should be removed from this proposal.

[fabiorocha]

I agree with the consensus of removing the title and icon members from the proposal. It should be easy to have them proposed to a later iteration if there's a strong enough need backed up by data.

I'll put up a PR shortly to remove those.