Removed unused member variable from GafferUI::Tool.
Removed unused member variable from GafferUI::Tool.

Caught by that nice young Mr Clang and his friend Mr Travis.

johnhaddon/gaffer,johnhaddon/gaffer,lucienfostier/gaffer,appleseedhq/gaffer,boberfly/gaffer,johnhaddon/gaffer,lucienfostier/gaffer,cedriclaunay/gaffer,ivanimanishi/gaffer,ivanimanishi/gaffer,hradec/gaffer,GafferHQ/gaffer,goddardl/gaffer,GafferHQ/gaffer,goddardl/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,hradec/gaffer,ImageEngine/gaffer,ImageEngine/gaffer,cedriclaunay/gaffer,johnhaddon/gaffer,hradec/gaffer,goddardl/gaffer,chippey/gaffer,ivanimanishi/gaffer,chippey/gaffer,cedriclaunay/gaffer,chippey/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,appleseedhq/gaffer,boberfly/gaffer,appleseedhq/gaffer,lucienfostier/gaffer,hradec/gaffer,ImageEngine/gaffer,chippey/gaffer,andrewkaufman/gaffer,boberfly/gaffer,cedriclaunay/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,hradec/gaffer,boberfly/gaffer,GafferHQ/gaffer,ivanimanishi/gaffer,appleseedhq/gaffer,ImageEngine/gaffer,goddardl/gaffer,andrewkaufman/gaffer