refactor!: remove deprecated GridFS API

removed all tests and code relating to the deprecated GridFS API
See the streaming GridFS API

NODE-2320

Author: nbbeeken

index.js

@@ -23,8 +23,6 @@ connect.MongoClient = require('./lib/mongo_client');
 connect.Db = require('./lib/db');
 connect.Collection = require('./lib/collection');
 connect.ReadPreference = require('./lib/read_preference');
-connect.GridStore = require('./lib/gridfs/grid_store');
-connect.Chunk = require('./lib/gridfs/chunk');
 connect.Logger = require('./lib/logger');
 connect.AggregationCursor = AggregationCursor;
 connect.CommandCursor = CommandCursor;