E2E: Unwedge olm sessions broken due to duplicated OTKs

[manuroe]

Because of a wrong OTK uploaded to the server (#3721, #3817), devices may not able to establish valid olm sessions between them.
The olm unwedge mechanism seems not to work in this case.

The scenario is:

• Bob succeeds (unfortunately) to publish a duplicate OTK (badBobOTK)
• Alice sends a message to Bob. She shares the new megom key using a new olm session based on badBobOTK
• Bob fails to start this inbound olm session (with error BAD_MESSAGE_KEY_ID)
• Bob cannot get the megolm key for the the olm message
• Bob cannot decode Alice's message
• All messages sent by Alice will be undecryptable for Bob. The olm session stays broken forever.

[manuroe]

The olm session unwedge mechanism does not work because it can retry using another bad OTK.

We are going to make the crypto module purge all its published OTKs in the next version to restart with a sane state.