Delete values from DataContext

[ARMmaster17]

Is your feature request related to a problem? Please describe.
Sometimes there can be a lot of data being passed through a pipeline. Once the data has been processed, it would result in better performance if the data was removed from the context. This will especially be important in #60 where there are network bandwidth limits to consider when sending context objects to other nodes.

Describe the solution you'd like
Add a delete(key: str) -> None function that removes a value from a context.