Remove the icon since it's defined by the app itself

Signed-off-by: Joas Schilling <coding@schilljs.com>

settings/css/settings.css

@@ -20,9 +20,6 @@ input#openid, input#webdav { width:20em; }
 .nav-icon-clientsbox {
 	background-image: url('../img/change.svg?v=1');
 }
-.nav-icon-activity {
-	background-image: url('../img/activity-dark.svg?v=1');
-}
 .nav-icon-federated-cloud {
 	background-image: url('../img/share.svg?v=1');
 }

settings/img/activity-dark.svg

@@ -1,4 +0,0 @@
-<?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<svg xmlns="http://www.w3.org/2000/svg" height="32" width="32" version="1.0">
- <path d="m16 1-10 18h11l-1 12 10-18h-11z"/>
-</svg>