IECoreArnoldPreview : Remove unused lambda captures
IECoreArnoldPreview : Remove unused lambda captures

Fixes OSX build:
 src/GafferArnold/IECoreArnoldPreview/Renderer.cpp:2530:4: error: lambda capture 'this' is not used [-Werror,-Wunused-lambda-capture]

ImageEngine/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,hradec/gaffer,GafferHQ/gaffer,boberfly/gaffer,GafferHQ/gaffer,lucienfostier/gaffer,boberfly/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,GafferHQ/gaffer,hradec/gaffer,hradec/gaffer,boberfly/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,appleseedhq/gaffer,lucienfostier/gaffer,johnhaddon/gaffer,hradec/gaffer,hradec/gaffer,andrewkaufman/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,appleseedhq/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,boberfly/gaffer,appleseedhq/gaffer,appleseedhq/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,johnhaddon/gaffer