pass only the routing key part in bucketization callback
pass only the routing key part in bucketization callback

Summary: as title. Most likely this is a noop change since we expect WhUpdates not to contain keys with routing prefixes, but for safety let's explicitly provide keys without routing prefixes.

Reviewed By: stuclar

Differential Revision: D40291737

fbshipit-source-id: 02fd26dcd796081a96db712634d29fab00e7f005

facebook/mcrouter,facebook/mcrouter,facebook/mcrouter,facebook/mcrouter