mac: remove libc++-static 10.6 compatibility hack

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 17dee6d9d8efeed35b948f6282ef18b23e2cc038..237afc46d4d02510d39518e6e5229f2cfa0415ae 100644
--- a/DEPS
+++ b/DEPS
@@ -865,18 +865,6 @@ hooks = [
                 '-s', 'src/buildtools/linux64/clang-format.sha1',
     ],
   },
-  # Pull the prebuilt libc++ static library for mac.
-  {
-    'name': 'libcpp_mac',
-    'pattern': '.',
-    'action': [ 'download_from_google_storage',
-                '--no_resume',
-                '--platform=darwin',
-                '--no_auth',
-                '--bucket', 'chromium-libcpp',
-                '-s', 'src/third_party/libc++-static/libc++.a.sha1',
-    ],
-  },
   # Pull luci-go binaries (isolate, swarming) using checked-in hashes.
   {
     'name': 'luci-go_win',