Be consistent with BotKit api

[imjul1an]

By default, BotKit implements delete on local storage.users object https://github.com/howdyai/botkit/blob/master/lib/storage/simple_storage.js#L73

Botkit-starage-redis has a different implementation, https://github.com/howdyai/botkit-storage-redis/blob/master/src/index.js#L51. Instead of delete we have remove.

A proposal is to rename the remove function to delete function. But, in your case, it would make more sense to support both remove and delete for backward compatibility.

So it would be nice to keep an API consistent with the BotKit.