Lazyloading for comment meta and term meta, introduced into `WP_Query` in
4.4, used flags - `updated_term_meta_cache` and `updated_comment_meta_cache` -
in an attempt to prevent cache priming from happening more than once per query
object. This technique was mostly effective, but not entirely efficient, since
the flag didn't prevent the `lazyload_*_meta` callbacks from running. The
obvious solution - removing the filter callback after it'd be run once - was
dismissed for 4.4 because of concerns that `remove_filter()` could disable
lazyloading too generally in the context of nested queries, due to the way
`_wp_filter_build_unique_id()` doesn't always build sufficiently unique IDs for
similar objects. However, further testing shows that this concern is only valid
in a very small subset of cases, while the cost of keeping the query objects in
memory, via the `$wp_filter` global, is quite significant. As such, this
changeset removes the flags in favor of the `remove_filter()` technique.
See #35454, #35816.
git-svn-id: https://develop.svn.wordpress.org/trunk@36524 602fd350-edb4-49c9-b593-d223f7449a82
d03ae82c32