Delete SassSpecRunner#for_current_impl?
Delete SassSpecRunner#for_current_impl?

We no longer use impl-specific directories.

nschonni/sass-spec,nschonni/sass-spec,sass/sass-spec,mgreter/sass-spec,sass/sass-spec,sass/sass-spec,mgreter/sass-spec,sass/sass-spec,nschonni/sass-spec,mgreter/sass-spec,nschonni/sass-spec