Revert rG6a605b97a200 due to excessive memory use

Over in the comments for D116821, some use-cases have cropped up where
there's a substantial increase in memory usage. A quick inspection
shows that a) it's a lot of memory and b) there are several things to
be done to reduce it. Reverting (via disabling this feature by default)
to avoid bothering people in the meantime.