This article explains in detail why and when you need fastclick.js:
https://developers.google.com/web/updates/2013/12/300ms-tap-delay-gone-away
TL;DR
As of Chrome 32 (back in 2014) this delay is gone for mobile-optimised sites, without removing pinch-zooming! Firefox and IE/Edge did the same shortly afterwards, and in March 2016 a similar fix landed in iOS 9.3.
As long as your <head> includes: <meta name="viewport" content="width=device-width">, this way the browser assumes you have made the text readable on mobile so there is no need for double-click.