feat(NODE-4079): estimated document count uses count

Author: durran

src/operations/estimated_document_count.ts

@@ -36,9 +36,8 @@ export class EstimatedDocumentCountOperation extends CommandOperation<number> {
     if (maxWireVersion(server) < 12) {
       return this.executeLegacy(server, session, callback);
     }
-    const pipeline = [{ $collStats: { count: {} } }, { $group: { _id: 1, n: { $sum: '$count' } } }];
 
-    const cmd: Document = { aggregate: this.collectionName, pipeline, cursor: {} };
+    const cmd: Document = { count: this.collectionName } };
 
     if (typeof this.options.maxTimeMS === 'number') {
       cmd.maxTimeMS = this.options.maxTimeMS;