Partially revert [27101], [27102], [27141], and [27142]. Those commits introduced new functions to sync up cache invalidation events. The current commit alters existing internals.

"The cache invalidation with static was introduced in r9102 with version 2.7. Multisite wasn't in core back then, so something like switch_to_blog() wasn't a concern, but now it breaks if you switch the blog in between calls to clean_term_cache."

This solution is simpler. All unit tests pass. Removes unnecessary tests linked to removed functions.

Props kovshenin.
Fixes #14485, #22526.


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