Remove unused constant.

Remove unused LOG_ERROR constant.

This constant has no other uses in cakephp/cakephp or in cakephp/app.
I'm pretty sure it is entirely unused at this point.

tests/bootstrap.php

@@ -34,7 +34,6 @@ define('CAKE', CORE_PATH . 'src' . DS);
 define('CORE_TESTS', CORE_PATH . 'tests' . DS);
 define('CORE_TEST_CASES', CORE_TESTS . 'TestCase');
 define('TEST_APP', CORE_TESTS . 'test_app' . DS);
-define('LOG_ERROR', LOG_ERR);
 
 // Point app constants to the test app.
 define('APP', TEST_APP . 'TestApp' . DS);