infra: Remove all references to the OSX 10.10 SDK.

scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_Mac10_9.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromium.webkit",
       "--builder",
       "WebKit Mac10.9",
@@ skipping 95 matching lines @@
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
-      "GYP_DEFINES": "clang=1 component=static_library gomadir='[BUILD]/goma' mac_sdk_min=10.10 target_arch=x64 test_isolation_mode=prepare use_goma=1"
+      "GYP_DEFINES": "clang=1 component=static_library gomadir='[BUILD]/goma' target_arch=x64 test_isolation_mode=prepare use_goma=1"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "[SLAVE_BUILD]/src/testing/buildbot/chromium.webkit.json",
       "/path/to/tmp/json"
@@ skipping 293 matching lines @@
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "Upload to test-results [browser_tests]"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]