Use files in path['checkout'] not resource.

scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_mac_swarming.json

 [
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/ios/host_info.py",
       "--json-file",
       "/path/to/tmp/json"
     ],
     "name": "host and tools info",
     "~followup_annotations": [
       "@@@STEP_TEXT@<br />OS X 1.2.3, Xcode 6.7.8 (5D342509a)@@@",
@@ skipping 292 matching lines @@
     "name": "compile",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output (invalid)@null@@@",
       "@@@STEP_LOG_END@json.output (invalid)@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
-      "RECIPE_MODULE[build::isolate]/resources/remove_build_metadata.py",
+      "[BUILDER_CACHE]/mac_swarming/src/tools/determinism/remove_build_metadata.py",
       "--build-dir",
-      "[BUILDER_CACHE]/mac_swarming/src/out/Debug",
-      "--src-dir",
-      "[BUILDER_CACHE]/mac_swarming/src"
+      "[BUILDER_CACHE]/mac_swarming/src/out/Debug"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "remove_build_metadata"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::isolate]/resources/isolate.py",
       "[BUILDER_CACHE]/mac_swarming/src/tools/swarming_client",
@@ skipping 2190 matching lines @@
       "@@@STEP_LOG_END@json.output@@@",
       "@@@STEP_LINK@shard #0 isolated out@blah@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]