remove selfclosing <switch/>

[JoKalliauer]

Same source as in RazrFalcon/resvg#363 (comment)

input=output

<?xml version="1.0" encoding="UTF-8"?>
<svg enable-background="new -491.5 -522.36 1638.55 1852.41" height="1852.41" viewBox="-491.5,-522.36,1638.55,1852.41" width="1638.55" xmlns="http://www.w3.org/2000/svg">
 <switch/>
</svg>

desired output

<?xml version="1.0" encoding="UTF-8"?>
<svg enable-background="new -491.5 -522.36 1638.55 1852.41" height="1852.41" viewBox="-491.5,-522.36,1638.55,1852.41" width="1638.55" xmlns="http://www.w3.org/2000/svg"/>