Remove apparently superfluous modules in requirements.txt

[shaycrk]

It seems like the requirements.txt file here should contain just those requirements required to compile and serve the documentation, but there are many packages like sklearn, spacy, psycopg2-binary that seem unlikely to be needed for that task (but perhaps are related to example code/notebooks provided here). It may be helpful to provide a requirements file for running the code examples, but that should be separate from the main requirements file for the repo itself.