Example using extractor interfaces are not finished

[hunterhector]

Describe the bug There are two main examples using the extractor interfaces:

1. https://github.com/asyml/forte/tree/master/examples/tagging
2. https://github.com/asyml/forte/tree/master/examples/srl

The first one did not load the vocabulary during validation and testing. The second one did not fully implement the relation extractor.

Expected behavior Both example should run and produce the same results as prior experiments

Screenshots If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 22]
• Python and Package verions: [e.g. Python version, Pytorch version]

Additional context These are due to half-interface changes during the extractor update. For a current working extractor usage, see: https://github.com/petuum/composing_information_system/blob/main/training.md