Enable svgo removeXMLNS plugin by default

This plugin removes the `xmlns` attribute from the top-level svg element, which is safe for inline SVGs, which is how all SVGs transformed by this plugin will end up being used. I think it makes sense to enable this plugin by default.

https://github.com/svg/svgo/blob/master/plugins/removeXMLNS.js

Locate the SVGO configuration or entry point and any existing SVG optimization tests; use the linked removeXMLNS.js behavior as the reference. Verify the default configuration includes this plugin and run the relevant test suite, confirming that transformed inline SVG output no longer retains the top-level xmlns attribute.

Written by the indexing model from the issue text.