Cleanup: remove support for launcher icons before SDK26.

Part of #2108.

src/main/res/drawable-v26/ic_launcher.xml

@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
-    <background android:drawable="@color/ic_launcher_background" />
-    <foreground android:drawable="@drawable/ic_logo_color_108dp" />
-    <monochrome android:drawable="@drawable/ic_logo_color_108dp" />
-</adaptive-icon>

src/main/res/drawable/ic_launcher.xml

@@ -1,3 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
-<inset xmlns:android="http://schemas.android.com/apk/res/android"
-    android:drawable="@drawable/ic_logo_color_24dp" />
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@color/ic_launcher_background" />
+    <foreground android:drawable="@drawable/ic_logo_color_108dp" />
+    <monochrome android:drawable="@drawable/ic_logo_color_108dp" />
+</adaptive-icon>

src/reproducible/res/drawable-v26/ic_launcher.xml

@@ -1,14 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
-    <background android:drawable="@color/ic_launcher_background" />
-    <foreground>
-        <inset
-            android:inset="20dp"
-            android:drawable="@drawable/ic_logo_24dp" />
-    </foreground>
-    <monochrome>
-        <inset
-            android:inset="20dp"
-            android:drawable="@drawable/ic_logo_24dp" />
-    </monochrome>
-</adaptive-icon>

src/reproducible/res/drawable/ic_launcher.xml

@@ -1,3 +1,14 @@
 <?xml version="1.0" encoding="utf-8"?>
-<inset xmlns:android="http://schemas.android.com/apk/res/android"
-    android:drawable="@drawable/ic_logo_108dp" />
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@color/ic_launcher_background" />
+    <foreground>
+        <inset
+            android:inset="20dp"
+            android:drawable="@drawable/ic_logo_24dp" />
+    </foreground>
+    <monochrome>
+        <inset
+            android:inset="20dp"
+            android:drawable="@drawable/ic_logo_24dp" />
+    </monochrome>
+</adaptive-icon>