Disable automatic backups when a removable USB flash drive is used

as storage location.

The backup backoff time is not reliable for this as the system still
attempts to backup the magic @pm@ package without checking for the
backoff value.
diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index fdded5e..14914e4 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -19,6 +19,11 @@
         android:name="android.permission.MANAGE_USB"
         tools:ignore="ProtectedPermissions" />
 
+    <!-- This is needed to change system backup settings -->
+    <uses-permission
+        android:name="android.permission.WRITE_SECURE_SETTINGS"
+        tools:ignore="ProtectedPermissions" />
+
     <application
         android:name=".Backup"
         android:allowBackup="false"