remove docgen source and targets from build

utils/compiler/compiler.gyp

 # 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_dir': '../..',
   },
   'targets': [
     {
@@ skipping 18 matching lines @@
           ],
           'outputs': [
             '<(SHARED_INTERMEDIATE_DIR)/utils_wrapper.dart.snapshot',
             '<(SHARED_INTERMEDIATE_DIR)/dart2js.dart.snapshot',
           ],
           'action': [
             '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart<(EXECUTABLE_SUFFIX)',
             'create_snapshot.dart',
             '--output_dir=<(SHARED_INTERMEDIATE_DIR)',
             '--dart2js_main=pkg/compiler/lib/src/dart2js.dart',
-            '--docgen_main=pkg/docgen/bin/docgen.dart',
             '--package_root=<(PRODUCT_DIR)/packages/',
           ],
         },
       ],
     },
     # Other targets depend on dart2js files, but have to many inputs,
     # which causes issues on some platforms.
     # This target lists all the files in pkg/compiler,
     # and creates a single dart2js_files.stamp
     {
@@ skipping 12 matching lines @@
           ],
           'action': [
             'python', '../../tools/create_timestamp_file.py',
             '<@(_outputs)',
           ],
         },
       ],
     }
   ],
 }