Refresh lsif-node

Created by: efritz

No one on the team has a current working understanding of either msft/lsif-node or sourcegraph/lsif-node. That's kind of a problem! I've been going through the lisf-node code and simplifying/dropping features we don't currently use so that we can have an easier time maintaining and transferring knowledge about the indexer.

This effort should conclude by having an automated test suite for the indexer (currently, neither indexer version has any tests associated with it).