LayoutTests: Disable Mac 10.9 for now.

testing/buildbot/chromium.fyi.json

 {
   "Android Asan Builder Tests (dbg)": {
     "gtest_tests": [
       {
         "args": [
           "--tool=asan"
         ],
         "swarming": {
           "can_use_on_swarming_builders": false
         },
@@ skipping 12068 matching lines @@
             "got_revision_cp"
           ],
           "script": "//third_party/WebKit/Tools/Scripts/merge-layout-test-results"
         },
         "name": "webkit_layout_tests",
         "results_handler": "layout tests",
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
             {
-              "os": "Mac-10.9"
-            },
-            {
               "os": "Mac-10.12"
             },
             {
               "gpu": "8086:0a2e",
               "os": "Mac-10.12"
             }
           ],
           "shards": 8
         }
       }
@@ skipping 273 matching lines @@
         "test": "views_unittests"
       }
     ]
   },
   "Win Builder (ANGLE)": {
     "additional_compile_targets": [
       "all"
     ]
   }
 }