Clean up default-platform gyp defines

The files that are excluded do not exist at that location, so the rule
is not effective.

We'll first want to move the platform stuff into a separate library, so
I'm just removing those lines for now

BUG=v8:3015
R=dcarney@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/237053002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20727 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

tools/gyp/v8.gyp

@@ -1017,12 +1017,6 @@
             '<(icu_gyp_path):icudata',
           ],
         }],
-        ['v8_use_default_platform==0', {
-          'sources!': [
-            '../../src/default-platform.cc',
-            '../../src/default-platform.h',
-          ],
-        }],
         ['icu_use_data_file_flag==1', {
           'defines': ['ICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE'],
         }, { # else icu_use_data_file_flag !=1