change the FAQ to reflect fixed-rate pricing under "Can I delete old files to save space?"

[daira]

Zooko wrote:

"""
Can I delete old files to save space?

For now, it is not possible to remove data from the LAE
service. If you unlink a file, you lose your ability to access it,
but it does not free up the space in your S3 bucket, so you still
get charged for it.
"""

That's absolutely incorrect because customers no longer get charged per byte, but instead
a flat fee. So rewrite this answer to:

"""
Can I delete old files to save space?

You can unlink a file, and if you didn't save any copies of the link to it anywhere, then
it is effectively gone for good. You don't need to worry about saving space because Least
Authority charges you only a flat monthly fee for your usage.
"""