This commit reverts the functionality introduced in PR #26260
(later refined by #27175, #27190, #27508) in which filtering by
attribute using the layered nav widget was improved to handle the
cases of variations out of stock. The revert is a response to the
numerous problems reported by users in Woo 4.4 and 4.5
Not all the code has been reverted, only the code that resulted in
visible functionality changes. Thus, the code that generates
term relationships for variations is still in place to keep database
consistency and to keep the reverting changes to the minimum needed.
70a1cb2f1f