Forum action cleanup

If the font-size of the these two elements were set in ems or rems, I'd agree. But I've double-checked our [LMS-based font-size() mixin](https://github.com/edx/edx-platform/blob/gprice/forum-action-cleanup/lms%2Fstatic%2Fsass%2Fbase%2F_mixins.scss#L6) and it is only outputting font-sizes in px units of measurement now. 

With that said and the rest of the visual spacing of this part of the UI controlled in px units, I'd prefer this remain consistent and use px as well.