[milo] remove linkBase and calculate links directly.

milo/buildsource/swarming/expectations/build-timeout.json

 {
   "Summary": {
     "ParentLabel": {
       "Label": "infra-continuous-precise-32",
       "URL": "/buildbucket/estaab-infra-waterfall-test/infra-continuous-precise-32"
     },
     "Label": "2d8d62f6be545b10",
     "Status": "InfraFailure",
     "Banner": {
       "OS": [
@@ skipping 21 matching lines @@
     "MainLink": [
       {
         "Label": "Task 2d8d62f6be545b10",
         "URL": "https://example.com/task?id=2d8d62f6be545b10\u0026show_raw=1\u0026wide_logs=true"
       }
     ],
     "SubLink": [
       [
         {
           "Label": "stdout",
-          "URL": "foo/stdout"
+          "URL": "/swarming/task/build-timeout/stdout"
         }
       ]
     ],
     "Started": "2016-03-14T10:00:01.85071Z",
     "Finished": "2016-03-14T11:00:18.48602Z",
     "Duration": 3616635310000,
     "Type": "Recipe",
     "LevelsDeep": 0,
     "Verbosity": 2,
     "Text": [
       "Task timed out"
     ]
   },
   "SourceStamp": null,
   "Components": [
     {
       "Label": "recipe bootstrap",
       "Status": "Success",
       "MainLink": [
         {
           "Label": "stdout",
-          "URL": "foo/steps/recipe_bootstrap/0/stdout"
+          "URL": "/swarming/task/build-timeout/steps/recipe_bootstrap/0/stdout"
         }
       ],
       "Started": "2016-03-14T10:00:02Z",
       "Finished": "2016-03-14T10:00:04Z",
       "Duration": 2000000000,
       "Type": "Step",
       "LevelsDeep": 0,
       "Verbosity": 1,
       "Text": null
     },
     {
       "Label": "setup_build",
       "Status": "Success",
       "MainLink": [
         {
           "Label": "stdout",
-          "URL": "foo/steps/setup_build/0/stdout"
+          "URL": "/swarming/task/build-timeout/steps/setup_build/0/stdout"
         }
       ],
       "SubLink": [
         [
           {
             "Label": "run_recipe",
-            "URL": "foo/steps/setup_build/0/logs/run_recipe/0"
+            "URL": "/swarming/task/build-timeout/steps/setup_build/0/logs/run_recipe/0"
           }
         ]
       ],
       "Started": "2016-03-14T10:00:02Z",
       "Finished": "2016-03-14T10:00:03Z",
       "Duration": 1000000000,
       "Type": "Step",
       "LevelsDeep": 0,
       "Verbosity": 1,
       "Text": [
@@ skipping 40 matching lines @@
         },
         {
           "Key": "Exit Code",
           "Value": "-15"
         }
       ]
     }
   ],
   "Blame": null
 }