Removed old status file entry for fixed bug which is causing test failures.

tests/corelib_2/corelib_2.status

 # Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # All static_tests have expected compile-time errors.
 [ $strong && $compiler != dart2analyzer && $compiler != dartdevc ]
 core_runtime_types_static_test: MissingCompileTimeError
 string_base_vm_static_test: MissingCompileTimeError
 string_replace_static_test: MissingCompileTimeError
 string_static_test: MissingCompileTimeError
@@ skipping 142 matching lines @@
 string_static_test: MissingCompileTimeError
 symbol_test/04: MissingCompileTimeError
 
 [ ($compiler == none || $compiler == precompiler || $compiler == app_jit) && $runtime != drt ]
 symbol_test/02: MissingCompileTimeError # Issue 11669
 symbol_test/03: MissingCompileTimeError # Issue 11669
 symbol_test/04: MissingCompileTimeError
 
 [ $runtime == safari || $runtime == safarimobilesim ]
 string_trimlr_test/02: RuntimeError # Uses Unicode 6.2.0 or earlier.
-string_split_test: RuntimeError # Issue 21431
 
 [ $compiler == dart2js && $runtime == chromeOnAndroid ]
 string_trimlr_test/02: RuntimeError # Uses Unicode 6.2.0 or earlier.
 
 [ $compiler == dart2js && $runtime == drt ]
 string_trimlr_test/02: RuntimeError # Uses Unicode 6.2.0 or earlier.
 
 [ $compiler == dart2js && $runtime == safarimobilesim ]
 string_trimlr_test/01: Fail
 string_trimlr_test/02: RuntimeError # Uses Unicode 6.2.0 or earlier.
@@ skipping 24 matching lines @@
 [ $compiler == none && $runtime == drt ]
 string_from_environment2_test: Skip
 string_from_environment3_test: Skip
 string_from_environment_test: Skip
 
 [ $system == windows && $arch == x64 ]
 stopwatch_test: Skip  # Flaky test due to expected performance behaviour.
 
 [ $runtime == vm ]
 string_case_test/01: RuntimeError