dumpSymbols deprecation notice

[joemaller]

DumpSymbols is still being used to output the list of xlinked SVGs, so there's an unnecessary deprecation notice being output to the site footer:

<svg class="arrow"><use xlink:href="#arrow" href="#arrow"></use></svg>

[ ... ]

<!-- SVG:dumpSymbols is deprecated. View the full list of SVGs from the Rest API. -->
<svg xmlns='http://www.w3.org/2000/svg' style='display: none;'>
    <symbol id="arrow" viewBox="0 0 25 10"><path fill-rule="evenodd" d="M0 5.57.01 4.4c12.59.08 18.84.08 18.77 0V0L25 4.99 18.77 10l.01-4.43H0Z"/>
</symbol>
</svg>

The wp_footer hook is registered from the SVG class constructor.