Revert ObligationForest on beta branch#31851

Merged

brson merged 1 commit intorust-lang:betafrom

nikomatsakis:backport-pr-31349

Feb 25, 2016

Commits on Feb 23, 2016

Revert "Auto merge of #30533 - nikomatsakis:fulfillment-tree, r=aturon"
nikomatsakis
committed