style: Drop layout.css.scroll-behavior.property-enabled pref.
style: Drop layout.css.scroll-behavior.property-enabled pref.

It was enabled by default in bug 1041833 (for desktops) and
bug 1087562 (for Fennec).

Differential Revision: https://phabricator.services.mozilla.com/D15707

DominoTree/servo,emilio/servo,saneyuki/servo,KiChjang/servo,notriddle/servo,szeged/servo,emilio/servo,splav/servo,KiChjang/servo,KiChjang/servo,DominoTree/servo,paulrouget/servo,KiChjang/servo,szeged/servo,pyfisch/servo,szeged/servo,paulrouget/servo,KiChjang/servo,paulrouget/servo,emilio/servo,notriddle/servo,splav/servo,larsbergstrom/servo,notriddle/servo,pyfisch/servo,peterjoel/servo,peterjoel/servo,peterjoel/servo,notriddle/servo,saneyuki/servo,DominoTree/servo,saneyuki/servo,pyfisch/servo,larsbergstrom/servo,paulrouget/servo,splav/servo,saneyuki/servo,nnethercote/servo,nnethercote/servo,KiChjang/servo,paulrouget/servo,KiChjang/servo,saneyuki/servo,splav/servo,saneyuki/servo,larsbergstrom/servo,szeged/servo,saneyuki/servo,saneyuki/servo,peterjoel/servo,szeged/servo,larsbergstrom/servo,splav/servo,pyfisch/servo,splav/servo,KiChjang/servo,DominoTree/servo,szeged/servo,nnethercote/servo,larsbergstrom/servo,szeged/servo,peterjoel/servo,emilio/servo,notriddle/servo,nnethercote/servo,notriddle/servo,paulrouget/servo,DominoTree/servo,pyfisch/servo,notriddle/servo,nnethercote/servo,szeged/servo,KiChjang/servo,larsbergstrom/servo,paulrouget/servo,nnethercote/servo,DominoTree/servo,emilio/servo,pyfisch/servo,nnethercote/servo,nnethercote/servo,splav/servo,szeged/servo,szeged/servo,larsbergstrom/servo,DominoTree/servo,pyfisch/servo,notriddle/servo,saneyuki/servo,nnethercote/servo,paulrouget/servo,notriddle/servo,splav/servo,DominoTree/servo,larsbergstrom/servo,splav/servo,notriddle/servo,pyfisch/servo,paulrouget/servo,peterjoel/servo,peterjoel/servo,emilio/servo,peterjoel/servo,pyfisch/servo,splav/servo,KiChjang/servo,emilio/servo,saneyuki/servo,DominoTree/servo,peterjoel/servo,larsbergstrom/servo,larsbergstrom/servo,emilio/servo,pyfisch/servo,emilio/servo,emilio/servo,nnethercote/servo,DominoTree/servo,peterjoel/servo,paulrouget/servo