GODRIVER-647 Remove bson.NewDocument from docs

Some examples in the documentation were out of date.

Change-Id: Idb2f5cdab205d2f8fcb8920ab75bbf6c679ede96

Author: tfogo

mongo/cursor.go

@@ -22,7 +22,7 @@ import (
 //		defer cur.Close(ctx)
 //
 // 		for cur.Next(ctx) {
-//			elem := bson.NewDocument()
+//			elem := &bson.D{}
 //			if err := cur.Decode(elem); err != nil {
 // 				log.Fatal(err)
 // 			}

mongo/doc.go

@@ -50,7 +50,6 @@
 // 	  	Foo string
 // 	  	Bar int32
 // 	  }{}
-//    result := bson.Raw{}
 //    filter := bson.D{{"hello", "world"}}
 //    err := collection.FindOne(context.Background(), filter).Decode(&result))
 //    if err != nil { return err }