At the moment, we have a concept of evict_priority to make metadata file pages "stick" to the cache until we're evicting aggressively.

This is hard to get right and sometimes causes us trouble. A recent example is WT-6499 where the metadata file pages were solely responsible for eviction kicking into gear but this "stickiness" factor stopped them from getting evicted below our target.

We should explore whether it's reasonable to remove evict_priority and whether we're still getting real performance gains with this technique.