[fenix] For https://github.com/mozilla-mobile/fenix/issues/537: Removes unused asset

app/src/main/res/drawable/rounded_button.xml

@@ -1,11 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!-- This Source Code Form is subject to the terms of the Mozilla Public
-   - License, v. 2.0. If a copy of the MPL was not distributed with this
-   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
-
-<shape xmlns:android="http://schemas.android.com/apk/res/android"
-       android:shape="oval">
-
-    <corners android:radius="60dp"/>
-    <solid android:color="@color/private_browsing_primary" />
-</shape>