removeFact (factOrId) {
    let factId
    if (!(factOrId instanceof Fact)) {
      factId = factOrId
    } else {
      factId = factOrId.id
    }

    return this.facts.delete(factId)
  }
Remove a fact definition to the engine.  Facts are called by rules as they are evaluated.
@param {object|Fact} id - fact identifier or instance of Fact