Remove LayoutTests/perf and associated references

LayoutTests/perf/array-nested-loop.html

-<script src="../resources/magnitude-perf.js"></script>
-<script>
-function setupFunction(magnitude)
-{
-    array = [];
-    for (var i = 0; i < magnitude; i++) {
-        array[i] = i;
-    }
-}
-
-function test(magnitude)
-{
-    for (var i = 0; i < array.length; i++) {
-        for (var j = 0; j < array.length; j++) {
-            var foo = array[i] + array[j];
-        }
-    }
-}
-
-Magnitude.description("Tests that doing a nested loop over an array is quadratic.");
-// Quite noisy
-// lax settings ok as simply verifying "significantly superlinear"
-Magnitude.initialExponent = 9;
-Magnitude.numPoints = 3;
-Magnitude.numTrials = 8;
-Magnitude.successThreshold = 0.25; // 2 out of 8
-Magnitude.tolerance = 0.40;
-Magnitude.run(setupFunction, test, Magnitude.POLYNOMIAL);
-</script>