Revert of [SVG] Implement 'discard' element

LayoutTests/svg/animations/script-tests/discard-on-discard.js

-description("Test the behavior of one discard applied on another discard");
-embedSVGTestCase("resources/discard-on-discard.svg");
-
-// Setup animation test
-function sample1() {
-    expectFillColor(rect1, 255, 0, 0);
-}
-
-function sample2() {
-    expectFillColor(rect1, 0, 255, 0);
-}
-
-function executeTest() {
-    var rects = rootSVGElement.ownerDocument.getElementsByTagName("rect");
-    rect1 = rects[0];
-
-    const expectedValues = [
-        // [animationId, time, sampleCallback]
-        ["anim", 0.0,   sample1],
-        ["anim", 0.01,   sample1],
-        ["anim", 2.0,   sample2],
-        ["anim", 2.01,   sample2],
-        ["anim", 3.0,   sample2],
-        ["anim", 3.01,   sample2]
-    ];
-
-    runAnimationTest(expectedValues);
-}
-
-window.animationStartsImmediately = true;
-var successfullyParsed = true;