Profiles advertise broken oembed endpoints

[tellyworth]

Profiles currently advertise two oembed endpoints:

<link rel="alternate" type="application/json+oembed" href="https://profiles.wordpress.org/wp-json/oembed/1.0/embed?url" />
<link rel="alternate" type="text/xml+oembed" href="https://profiles.wordpress.org/wp-json/oembed/1.0/embed?url&#038;format=xml" />

Neither of these seem to work. Both produce output like this, regardless of the URL parameter:

{"code":"oembed_invalid_url","message":"Not Found","data":{"status":404}}

Ideally, we should make oembed work.
Worst case, stop advertising broken links.

Loosely related: #613.