External: remove &block arg, use block_given?
External: remove &block arg, use block_given?

Addresses my comment in https://github.com/jekyll/jekyll/pull/4936#discussion_r64598949

nasht00/jekyll,getandpost/jekyll.github.io,Strangehill/jekyll,gencer/jekyll,getandpost/jekyll.github.io,tomjohnson1492/jekyll,Strangehill/jekyll,rlugojr/jekyll,rlugojr/jekyll,pmarsceill/jekyll,gencer/jekyll,ryanshaw/jekyll,Strangehill/jekyll,nasht00/jekyll,stomar/jekyll,fulldecent/jekyll,rasa2011/rasa2011.github.io,stomar/jekyll,xcatliu/jekyllcn,alfredxing/jekyll,fulldecent/jekyll,alfredxing/jekyll,jaybe-jekyll/jekyll,pmarsceill/jekyll,tillgrallert/jekyll,jekyll/jekyll,floydpraveen/jekyll,chrisfinazzo/jekyll,rasa2011/rasa2011.github.io,alfredxing/jekyll,chrisfinazzo/jekyll,ryanshaw/jekyll,darwin/jekyll,tomjohnson1492/jekyll,stomar/jekyll,jeffkole/jekyll,rlugojr/jekyll,darwin/jekyll,tomjohnson1492/jekyll,jeffkole/jekyll,fulldecent/jekyll,Strangehill/jekyll,jaybe-jekyll/jekyll,floydpraveen/jekyll,tillgrallert/jekyll,derekgottlieb/jekyll,getandpost/jekyll.github.io,xiebinhqy/jklly_china,jekyll/jekyll,rasa2011/rasa2011.github.io,xcatliu/jekyllcn,tillgrallert/jekyll,xiebinhqy/jklly_china,jekyll/jekyll,ZDroid/jekyll,ryanshaw/jekyll,xcatliu/jekyllcn,nasht00/jekyll,ZDroid/jekyll,alfredxing/jekyll,noikiy/jekyll,tomjohnson1492/jekyll,jekyll/jekyll,noikiy/jekyll,tomjohnson1492/jekyll,Strangehill/jekyll,ryanshaw/jekyll,floydpraveen/jekyll,alex-kovac/jekyll,gencer/jekyll,ZDroid/jekyll,alex-kovac/jekyll,nasht00/jekyll,tillgrallert/jekyll,rlugojr/jekyll,derekgottlieb/jekyll,darwin/jekyll,noikiy/jekyll,fulldecent/jekyll,stomar/jekyll,derekgottlieb/jekyll,darwin/jekyll,jaybe-jekyll/jekyll,noikiy/jekyll,alex-kovac/jekyll,tillgrallert/jekyll,floydpraveen/jekyll,xcatliu/jekyllcn,alex-kovac/jekyll,xiebinhqy/jklly_china,yhironaka/yhironaka.github.io,x-way/jekyll,x-way/jekyll,gencer/jekyll,jaybe-jekyll/jekyll,jeffkole/jekyll,x-way/jekyll,chrisfinazzo/jekyll,jeffkole/jekyll,xiebinhqy/jklly_china,pmarsceill/jekyll,pmarsceill/jekyll,x-way/jekyll,chrisfinazzo/jekyll,derekgottlieb/jekyll,gencer/jekyll,alex-kovac/jekyll