Milo: Remove swarming tags from build properties

milo/appengine/swarming/expectations/build-exception.json

 {
   "Summary": {
-    "ParentLabel": null,
     "Label": "2d8d62f6be545b10",
     "Status": "Failure",
-    "Banner": null,
-    "Bot": null,
     "Source": {
       "Label": "Task 2d8d62f6be545b10",
       "URL": "https://example.com/user/task/2d8d62f6be545b10"
     },
     "MainLink": {
       "Label": "Task 2d8d62f6be545b10",
       "URL": "https://example.com/user/task/2d8d62f6be545b10"
     },
     "SubLink": [
       {
         "Label": "stdout",
         "URL": "foo/stdout"
       }
     ],
-    "Progress": null,
     "Started": "2016-03-14T10:00:01.85071Z",
     "Finished": "2016-03-14T11:00:18.48602Z",
     "Duration": 3616635310000,
     "Type": "Recipe",
     "LevelsDeep": 0,
     "Verbosity": 2,
     "Text": [
       "InfraFailure bot_update",
       "InfraFailure Uncaught Exception"
     ]
   },
   "SourceStamp": null,
   "Components": [
     {
-      "ParentLabel": null,
       "Label": "recipe bootstrap",
       "Status": "Success",
-      "Banner": null,
-      "Bot": null,
-      "Source": null,
       "MainLink": {
         "Label": "stdout",
         "URL": "foo/steps/recipe_bootstrap/0/stdout"
       },
-      "SubLink": null,
-      "Progress": null,
       "Started": "2016-03-14T10:00:02Z",
       "Finished": "2016-03-14T10:00:09Z",
       "Duration": 7000000000,
       "Type": "Step",
       "LevelsDeep": 0,
       "Verbosity": 1,
       "Text": null
     },
     {
-      "ParentLabel": null,
       "Label": "setup_build",
       "Status": "Success",
-      "Banner": null,
-      "Bot": null,
-      "Source": null,
       "MainLink": {
         "Label": "stdout",
         "URL": "foo/steps/setup_build/0/stdout"
       },
       "SubLink": [
         {
           "Label": "run_recipe",
           "URL": "foo/steps/setup_build/0/logs/run_recipe/0"
         }
       ],
-      "Progress": null,
       "Started": "2016-03-14T10:00:03Z",
       "Finished": "2016-03-14T10:00:04Z",
       "Duration": 1000000000,
       "Type": "Step",
       "LevelsDeep": 0,
       "Verbosity": 1,
       "Text": [
         "running recipe: \"v8\""
       ]
     },
     {
-      "ParentLabel": null,
       "Label": "bot_update",
       "Status": "InfraFailure",
-      "Banner": null,
-      "Bot": null,
-      "Source": null,
       "MainLink": {
         "Label": "stdout",
         "URL": "foo/steps/bot_update/0/stdout"
       },
       "SubLink": [
         {
           "Label": "json.output (invalid)",
           "URL": "foo/steps/bot_update/0/logs/json.output__invalid_/0"
         }
       ],
-      "Progress": null,
       "Started": "2016-03-14T10:00:05Z",
       "Finished": "2016-03-14T10:00:06Z",
       "Duration": 1000000000,
       "Type": "Step",
       "LevelsDeep": 0,
       "Verbosity": 2,
       "Text": null
     },
     {
-      "ParentLabel": null,
       "Label": "Uncaught Exception",
       "Status": "InfraFailure",
-      "Banner": null,
-      "Bot": null,
-      "Source": null,
       "MainLink": {
         "Label": "stdout",
         "URL": "foo/steps/Uncaught_Exception/0/stdout"
       },
       "SubLink": [
         {
           "Label": "exception",
           "URL": "foo/steps/Uncaught_Exception/0/logs/exception/0"
         }
       ],
-      "Progress": null,
       "Started": "2016-03-14T10:00:07Z",
       "Finished": "2016-03-14T10:00:08Z",
       "Duration": 1000000000,
       "Type": "Step",
       "LevelsDeep": 0,
       "Verbosity": 2,
       "Text": null
     }
   ],
   "PropertyGroup": [
@@ skipping 35 matching lines @@
       "Property": null
     },
     {
       "GroupName": "Swarming",
       "Property": [
         {
           "Key": "Exit Code",
           "Value": "0"
         }
       ]
-    },
-    {
-      "GroupName": "Swarming Tags",
-      "Property": [
-        {
-          "Key": "allow_milo",
-          "Value": "1"
-        }
-      ]
     }
   ],
   "Blame": null
 }