Add a helper function to delete data from Cache Storage

[hammer-ai]

Hi there, it would be great if we could add a helper to delete data from Cache Storage, as when we update models or model libs, the older versions seem to persist. Thank you!

[tqchen]

cc @CharlieFRuan , indeed this would be useful, we should be able to do caches.delete("webllm/model") etc to remove these, but good to make them explicit as well in webllm

[DiegoCao]

Hi, the function to delete cache is included in src/cache_util.ts