* `RegistrationHandler.appservice_register` no longer issues an access token:
instead it is left for the caller to do it. (There are two of these, one in
`synapse/rest/client/v1/register.py`, which now simply calls
`AuthHandler.issue_access_token`, and the other in
`synapse/rest/client/v2_alpha/register.py`, which is covered below).
* In `synapse/rest/client/v2_alpha/register.py`, move the generation of
access_tokens into `_create_registration_details`. This means that the normal
flow no longer needs to call `AuthHandler.issue_access_token`; the
shared-secret flow can tell `RegistrationHandler.register` not to generate a
token; and the appservice flow continues to work despite the above change.
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