Use system fonts instead of Robot webfont

Fixes #449

less/bootstrap/variables.less

@@ -42,7 +42,7 @@
 //
 //## Font, line-height, and color for body text, headings, and more.
 
-@font-family-sans-serif:  "Roboto", "Helvetica Neue", Helvetica, Arial, sans-serif;
+@font-family-sans-serif:  -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
 @font-family-serif:       Georgia, "Times New Roman", Times, serif;
 //** Default monospace fonts for `<code>`, `<kbd>`, and `<pre>`.
 @font-family-monospace:   Menlo, Monaco, Consolas, "Courier New", monospace;

library.js

@@ -122,14 +122,4 @@ library.addUserToTopic = function(data, callback) {
 	}
 };
 
-library.getLinkTags = function (data, callback) {
-	data.links.push({
-		rel: 'prefetch stylesheet',
-		type: '',
-		href: 'https://fonts.googleapis.com/css?family=Roboto:300,400,500,700',
-	});
-
-	callback(null, data);
-};
-
 module.exports = library;

plugin.json

@@ -7,8 +7,7 @@
 		{ "hook": "filter:config.get", "method": "getThemeConfig" },
 		{ "hook": "static:app.load", "method": "init" },
 		{ "hook": "filter:admin.header.build", "method": "addAdminNavigation" },
-		{ "hook": "filter:topic.build", "method": "addUserToTopic" },
-		{ "hook": "filter:meta.getLinkTags", "method": "getLinkTags"}
+		{ "hook": "filter:topic.build", "method": "addUserToTopic" }
 	],
 	"scripts": [
 		"lib/persona.js",