Yes, it is still in the 2014 Code:
1.9 It is for admission authorities to formulate their admission arrangements, but they must not:
j) in designated grammar schools that rank all children according to a pre-determined pass mark and then allocate places to those who score highest, give priority to siblings of current or former pupils;
I suspect that that paragraph is to stop the schools firstly offering places to those with siblings, irrespective of how high a score they passed with, then 'filling up' with those brighter children who happen not to have siblings in the school. Grammars are, after all, for the brightest children, not those who have a brighter sibling!
It could be argued (although I don't know of schools that so do) that schools might use siblings as a tie break amongst those of equal weighted points, along with distance from the school. It would of course only affect one or two children per year at the very bottom of the cut-off. Schools probably don't use it as j) appears to prohibit it - a side-effect of the much reduced admissions code a few years ago.