Change upload checkbox name and default in certify dialog, too

OpenKeychain/src/main/res/layout/certify_key_fragment.xml

@@ -62,7 +62,6 @@
             android:id="@+id/sign_key_upload_checkbox"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
-            android:checked="true"
             android:text="@string/label_send_key"
             android:paddingTop="12dp"
             android:paddingBottom="12dp"/>