Users with associated email addresses can't deactivate their accounts

[lampholder]

To reproduce:

• register a new user @test.user.32492374987:matrix.org with an email address [email protected]
• try and deactivate your account
• see an unknown error in the ux, that's actually a 400 {"errcode":"M_UNKNOWN","error":"Failed to remove threepid from ID server"}

[salcedo]

Getting the same error when trying to deactivate account or remove an associated email address. This is not cool. First there is an exposure - now we can't deactivate and get our data removed from the matrix HS.

[neilisfragile]

This is a sydent bug, tracking here matrix-org/sydent#145

[neilisfragile]

Closing in favour of matrix-org/sydent#145

@salcedo we have a temporary workaround live on the vector.im sydent, so you should be able to deactivate now.