Twenty Fourteen: Remove rem units from the style sheet

[iamtakashi]

Having rem units makes the style sheet really large because we need to have pixel fallbacks for all. Although Twenty Twelve uses it, Twenty Thirteen doesn't. I don't think we need to use the unit for Twenty Fourteen and removing it makes the style sheet much less confusing and smaller which is good for many ways.

We discussed in Twenty Fourteen office hours on 19th September. ​IRC Log.

[iamtakashi]

Remove rem units from the style sheet

[iamtakashi]

Updated patch that removes rem units also from rtl.css

[lancewillett]

In 25523:

Twenty Fourteen: remove rem units, props iamtakashi. Fixes #25366.