Remove ES2015 tests than do not parse in ES2016 (#4501)

These tests are originally from Traceur, which does not fully support
ES2016.

See babel/babylon#106 for a rationale why these code blocks are not
valid ES2016.

packages/babel-preset-es2015/test/fixtures/traceur/Misc/PrependStatement.js

@@ -9,10 +9,3 @@ var o = {
 function f({x}) {}
 f(o);
 assert.equal(1, count);
-
-count = 0;
-function g({x}) {
-  'use strict';
-}
-g(o);
-assert.equal(1, count);

packages/babel-preset-es2015/test/fixtures/traceur/Syntax/ParamDuplicateCheckOk.js

@@ -1,11 +1,3 @@
-function f(x, y = function(x) {}) {
-  'use strict';
-}
-
-var f2 = (x, y = function(x) {}) => {
-  'use strict';
-};
-
 function g() {
   'use strict';
   function h(x, y = function(x) {}) {