Bug 1723729 - Remove old Talos XPI generation scripts and documents. r=jmaher,perftest-reviewers,alexandru.irimovici

These documents and scripts were used to generate the add-ons for the tresize
and tart Talos tests before the great WebExtension conversion.

Nowadays, if people really want to install these tests locally, they can
go to about:debugging, use Load Temprary Add-on, and browse to the manifest
of the add-on folder.

Depends on D122378

Differential Revision: https://phabricator.services.mozilla.com/D122379