reaction.removed fires when a contact removes a reaction from one part of a message.
Read the payload
Thedata object is the ReactionEventBase schema from the API contract. The envelope around it is the same on every event and is described in the event catalog.
Handle the event
Remove the matching reaction from partpart_index of message message_id; the payload names the same reaction_type and from_handle the reaction.added event carried. Treat a removal for a reaction you never stored as already done.

