Element Web takes (up to) 30 seconds to send secrets after successful verification

[richvdh]

Steps to reproduce

1. Observe "Your key storage is out of sync" on EX:
   
2. Verify a against EW
3. Wait
4. Wait a bit longer
5. Banner is still there
6. Eventually, banner disappears

Outcome

The problem appears to be that, having received the m.secret.request, EW is waiting for a /sync timeout before it sends the reply.

[richvdh]

It would be better if the secrets were sent as part of the verification exchange (matrix-org/matrix-spec#2209), but we can make this much better in the meantime