Remove MIPS support

runtime/tools/gyp/runtime-configurations.gypi

 # Copyright (c) 2012, 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.
 
 {
   'variables': {
     'dart_debug_optimization_level%': '2',
     # If we have not set dart_io_support to 1 in Dart's all.gypi or common.gypi,
     # then do not build the native libraries supporting  dart:io.
     'dart_io_support%': 0,
@@ skipping 75 matching lines @@
         },
       },
 
       'Dart_simarmv5te_Base': {
         'abstract': 1,
         'xcode_settings': {
           'ARCHS': [ 'i386' ],
         },
       },
 
-      'Dart_simmips_Base': {
-        'abstract': 1,
-        'xcode_settings': {
-          'ARCHS': [ 'i386' ],
-        },
-      },
-
       'Dart_Debug': {
         'abstract': 1,
         'defines': [
           'DEBUG',
         ],
         'xcode_settings': {
           'GCC_OPTIMIZATION_LEVEL': '<(dart_debug_optimization_level)',
         },
       },
 
@@ skipping 12 matching lines @@
 
       'Dart_Product' : {
         'abstract': 1,
         'xcode_settings': {
           'GCC_OPTIMIZATION_LEVEL': '3',
         }
       },
     },
   },
 }