Delete perf tests that are WontFixed.

LayoutTests/perf/object-keys.html

-<script src="../resources/magnitude-perf.js"></script>
-<script>
-function setupFunction(magnitude)
-{
-    obj = {};
-    for (var i = 0; i < magnitude; i++) {
-        obj[i] = i;
-    }
-}
-
-function test(magnitude)
-{
-    Object.keys(obj);
-}
-
-Magnitude.description("Tests that Object.keys is linear.");
-Magnitude.numTrials = 5; // pretty noisy
-Magnitude.successThreshold = 0.40; // 2 out of 5
-Magnitude.initialExponent = 9;
-Magnitude.numPoints = 5;
-Magnitude.tolerance = 0.25; // 5%-25% deviations not uncommon
-Magnitude.trim = 1;
-Magnitude.run(setupFunction, test, Magnitude.LINEAR);
-</script>