Earlier quoted context omitted.
All 3rd party vendors have to include code for many features, websites, browsers and devices. They will always contain unused code. GA does a lot and it's doubtful you're using much of it.
They could at least gzip the damn thing or whatever their own pagespeed tool says is wrong with every asset loaded from Google
Pagespeed is a subpar tool that really shouldn't be used much. Follow the best practices and don't try to fix every possible little complaint.
As far as Google serving files though, its about as optimized as it gets. The JS file is gzip'd, served by Google's cloud network and on chrome it even uses their own QUIC protocol which is faster. It's also likely cached by the sheer amount of usage across the web so it'll probably be the fastest loading thing on your entire site.