Remove redundant and irrelevant tests

Two tests placed within the "variable" directory do not include a variable
declaration. Because the behavior they assert is covered by an existing
test (test/language/arguments-object/10.5-1gs.js), they may be removed
without reducing coverage.

test/language/statements/variable/12.2.1-13-s.js

@@ -1,13 +0,0 @@
-// Copyright (c) 2012 Ecma International.  All rights reserved.
-// This code is governed by the BSD license found in the LICENSE file.
-
-/*---
-es5id: 12.2.1-13-s
-description: arguments assignment throws SyntaxError in strict mode
-flags: [onlyStrict]
----*/
-
-
-assert.throws(SyntaxError, function() {
-    eval('function foo() { arguments = 42; }; foo()');
-});

test/language/statements/variable/12.2.1-15-s.js

@@ -1,15 +0,0 @@
-// Copyright (c) 2012 Ecma International.  All rights reserved.
-// This code is governed by the BSD license found in the LICENSE file.
-
-/*---
-es5id: 12.2.1-15-s
-description: >
-    arguments - a function expr assigning into 'arguments' throws a
-    SyntaxError in strict mode
-flags: [onlyStrict]
----*/
-
-
-assert.throws(SyntaxError, function() {
-    eval('(function () {arguments = 42;})()');
-});