ui/gfx: Remove duplicated win condition.

We already have the same msvs_disabled_warnings declared at line 172. No
need to have it twice.

BUG=331829
TEST=gfx_unittests
TBR=sky@chromium.org

Review URL: https://codereview.chromium.org/555543003

Cr-Commit-Position: refs/heads/master@{#294756}

ui/gfx/gfx_tests.gyp

@@ -90,10 +90,6 @@
         }, {  # OS != "ios"
           'sources': ['<@(_all_sources)'],
         }],
-        ['OS == "win"', {
-          # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
-          'msvs_disabled_warnings': [ 4267, ],
-        }],
         ['OS != "mac" and OS != "ios"', {
           'sources': [
             'transform_unittest.cc',