Remove the localStorage replication of the block cookie

Remove the localStorage replication of the block cookie

The block cookie was being replicated to localStorage in an attempt
to make it harder for users to get around the block by deleting the
cookie (and changing IP addresses).

This whole setup was hard to test, had a few bugs (e.g. the localStorage
value would never expire), and given that it is a minor improvement
over just a plain cookie, it is now being removed. The cookie is only
intended to stop casual block-evaders (other users will get around it
by deleting the cookie or using incognito mode) and so it is not felt
worth having the extra complexity that will only guard against people
who know to remove cookies, not use incognito mode, and yet don't know
to remove localStorage.

Bug: T152952
Change-Id: Ifb06dc2390f4d648d7fcb39e30267de5eddc6941