Make task returned by delete() method in StorageReference class in Firebase Storage cancellable

## What feature would you like to see?

Hi, would it be possible to make delete task in Firebase Storage cancellable the same way UploadTask is cancellable? At the moment delete() method returns abstract Task which is not possible to cancel.

## How would you use it?

In case there is no network connectivity and the user leaves activity where he/she wanted to perform deletion operation, I would like to cancel task in a similar fashion I cancel UploadTask before it gets executed by scheduler when network connection is back.