Fix useLegacyStretchBehaviour flag by simplifying its usage
Fix useLegacyStretchBehaviour flag by simplifying its usage

Summary: See blame revision. we are still passing all the added tests from that pull request but with much simpler logic.

Reviewed By: gkassabli

Differential Revision: D4977923

fbshipit-source-id: cb488e63c7c2e15e4c0f0133a16df36580c646fd

facebook/css-layout,yihuang/css-layout,yihuang/css-layout,facebook/css-layout,facebook/css-layout,yihuang/css-layout,facebook/yoga,facebook/css-layout,facebook/css-layout,facebook/css-layout,yihuang/css-layout,yihuang/css-layout,facebook/yoga,yihuang/css-layout,facebook/css-layout,facebook/yoga,facebook/yoga,facebook/yoga,yihuang/css-layout,yihuang/css-layout,yihuang/css-layout,facebook/yoga,facebook/yoga,facebook/css-layout,facebook/yoga,facebook/css-layout,facebook/yoga,yihuang/css-layout,facebook/yoga