In WT-3435 we made a change to cope with a rare situation where all pages in cache are clean but contain history that has to be maintained for reads. We can't evict those pages but also don't consider them for lookaside eviction, which led to tests hanging.

The approach taken was to dirty pages so ordinary eviction would consider them for lookaside. Dirtying pages randomly in eviction causes more problems than it is worth: revert it.