Remove jQuery Nicescroll
A 110KB dependency (which needs to be parsed before the JS can be used, regardless of gzip compression) for simple scrolling in the sidebar and a small handful of other places seems a bit much. Unless there's a very good argument for this being better than using the overflow-y property and browser-specific scrollbar overrides in CSS, I think we should remove it.
It was added in this commit. git grep 'nicescroll' and git grep 'niceScroll' gives me the following as the only places it's being used outside of jquery.nicescroll.js itself:
app/assets/javascripts/application.js.coffee:#= require jquery.nicescroll
app/assets/javascripts/application.js.coffee: $(".nicescroll").niceScroll(cursoropacitymax: '0.4', cursorcolor: '#FFF', cursorborder: "1px solid #FFF")
app/assets/javascripts/sidebar.js.coffee: niceScrollBars = $('.nicescroll').niceScroll();
app/views/layouts/_page.html.haml: .sidebar-wrapper.nicescroll{ class: nav_sidebar_class }
app/views/layouts/ci/_page.html.haml: .sidebar-wrapper.nicescroll{ class: nav_sidebar_class }
app/assets/javascripts/issuable_context.js.coffee: $(".right-sidebar").niceScroll()