Remove duplicated data from legacy events

When event-tracking was fully integrated into the platform, some data was replicated in the context in the middleware and then later extracted and moved the old location by event-tracking. The legacy code path was not updated to remove this transient shim data from the context resulting in duplication of the information. This patch ensures that the transient information is removed from the context before emitting the event.

Fixes: AN-2369
Merge pull request #4566 from mulby/remove-duplicate-context-fields

Remove duplicated data from legacy events