Drop support for kitkat; Bump minSdk to 21

This has been dead for a while already, remove the code and bump minSdk to a
version that actually works

Signed-off-by: Aayush Gupta <aayushgupta219@gmail.com>

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

@@ -0,0 +1,28 @@
+<!--
+  ~ Aurora Store
+  ~  Copyright (C) 2021, Rahul Kumar Patel <whyorean@gmail.com>
+  ~
+  ~  Aurora Store is free software: you can redistribute it and/or modify
+  ~  it under the terms of the GNU General Public License as published by
+  ~  the Free Software Foundation, either version 2 of the License, or
+  ~  (at your option) any later version.
+  ~
+  ~  Aurora Store is distributed in the hope that it will be useful,
+  ~  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  ~  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  ~  GNU General Public License for more details.
+  ~
+  ~  You should have received a copy of the GNU General Public License
+  ~  along with Aurora Store.  If not, see <http://www.gnu.org/licenses/>.
+  ~
+  -->
+
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="#FFF"
+        android:pathData="M7,8L7,6a5,5 0,1 1,10 0v2h3a1,1 0,0 1,1 1v12a1,1 0,0 1,-1 1L4,22a1,1 0,0 1,-1 -1L3,9a1,1 0,0 1,1 -1h3zM7,10L5,10v10h14L19,10h-2v2h-2v-2L9,10v2L7,12v-2zM9,8h6L15,6a3,3 0,0 0,-6 0v2z" />
+</vector>