[12.x] Remove all legacy code related to authorize.php and FileTransfer

Problem/Motivation

Split from 📌 Deprecate/remove the ability to update a module from a URL and authorize.php Active

This issue is for 12.x to (finally!) remove authorize.php, the FileTransfer classes, and the rest of the Updater classes.

Note that "update.module" is slightly a lie for component, since it's technically all code living in "base system", but it only exists for the legacy update manager and it's effectively part of update.module.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet