Don't auto-create contact portals for contacts that are logged-in matrix users

[maltee1]

We should assume that the user wants to talk to them on plain matrix rather than through signal, even if bridge.autocreate_contact_portal == True

[tulir]

Probably easier to remove the autocreate_contact_portal option 🤔

[maltee1]

Easier, yes, but it doesn't do what I want :)