Remove redundant tests

These tests are syntactically equivalent to
`test/language/statements/with/12.10.1-7-s.js` and may therefore be
removed without degrading coverage.

While `test/language/statements/with/12.10.1-9-s.js` differs slightly in
the pattern used to enable strict mode, the relevant behavior of the
"use strict" directive prologue is expressly tested via
`test/language/directive-prologue/func-expr-inside-func-decl-parse.js`.

test/language/statements/with/12.10.1-15-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: 12.10.1-15-s
-description: >
-    Strict Mode - SyntaxError is thrown when the RHS of a dot property
-    assignment utilizes WithStatement
-flags: [onlyStrict]
----*/
-
-
-assert.throws(SyntaxError, function() {
-            eval("var obj = {}; obj.get = function (a) { with(a){} }; ");
-});

test/language/statements/with/12.10.1-16-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: 12.10.1-16-s
-description: >
-    Strict Mode - SyntaxError is thrown when the RHS of an object
-    indexer assignment utilizes WithStatement
-flags: [onlyStrict]
----*/
-
-
-assert.throws(SyntaxError, function() {
-            eval("var obj = {}; obj['get'] = function (a) { with(a){} };  ");
-});

test/language/statements/with/12.10.1-9-s.js

@@ -1,21 +0,0 @@
-// Copyright (c) 2012 Ecma International.  All rights reserved.
-// This code is governed by the BSD license found in the LICENSE file.
-
-/*---
-es5id: 12.10.1-9-s
-description: >
-    with statement in strict mode throws SyntaxError (strict function
-    expression)
-flags: [noStrict]
----*/
-
-
-assert.throws(SyntaxError, function() {
-    eval("\
-          var f = function () {\
-                \'use strict\';\
-                var o = {}; \
-                with (o) {}; \
-              }\
-        ");
-});