LibWeb/SVG: Remove fixme about SVGSVGElement::getElementById()

Resolved in https://github.com/w3c/svgwg/commit/e02e2c64659238b6ea1434325579a88226e25d81

Libraries/LibWeb/SVG/SVGSVGElement.idl

@@ -29,7 +29,6 @@ interface SVGSVGElement : SVGGraphicsElement {
     SVGTransform createSVGTransform();
     [FIXME] SVGTransform createSVGTransformFromMatrix(optional DOMMatrix2DInit matrix = {});
 
-    // NOTE: The spec says this returns `Element` but that's a bug: https://github.com/w3c/svgwg/issues/923
     Element? getElementById(DOMString elementId);
 
     // Deprecated methods that have no effect when called,