Remove an outdated Firefox workaround

sindresorhus · sindresorhus · commit 32713e4f4689 · 2022-12-07T14:48:10.000+01:00
diff --git a/modern-normalize.css b/modern-normalize.css
@@ -42,7 +42,6 @@ body {
 	margin: 0; /* 1 */
 	font-family:
 		system-ui,
-		-apple-system, /* Firefox supports this but not yet `system-ui` */
 		'Segoe UI',
 		Roboto,
 		Helvetica,
