Example using extractor interfaces are not finished

**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