style: fixed an unused import warning.
style: fixed an unused import warning.

Differential Revision: https://phabricator.services.mozilla.com/D12028

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