Remove nonexisting function

[neon-dev]

Removed delete function of crate notifications, which is not implemented.

Maybe you want to consider renaming the hide function to delete in the next major version and add an option to decrement the unread count on delete. The current implementation for hide is not a real hide, since the message can't be unhidden (which is fine, except for the naming). Currently the only way to clear the crate notification icon without toggling the button is:

crate.store.dispatch({ type: 'REMOVE_NOTIFICATION', payload: { decrement: true } })