Update owners and milestones in flag-metadata.json

This CL updates two entries:
- enable-service-worker-imported-script-update-check
- enable-service-worker-servicification

Bug: 897809
Change-Id: I08103d8e247b8251a7aa62e5e7a30bab04c0cc94
Reviewed-on: https://chromium-review.googlesource.com/c/1341284
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609284}

chrome/browser/flag-metadata.json

@@ -1669,7 +1669,8 @@
   },
   {
     "name": "enable-service-worker-imported-script-update-check",
-    // "owners": [ "your-team" ],
+    "owners": [ "worker-dev@chromium.org" ],
+    // It's still in development. Tentatively set to M76 as the expiry_milestone.
     "expiry_milestone": 76
   },
   {
@@ -1679,8 +1680,9 @@
   },
   {
     "name": "enable-service-worker-servicification",
-    // "owners": [ "your-team" ],
-    "expiry_milestone": 76
+    "owners": [ "worker-dev@chromium.org" ],
+    // Enabled by default in M72.
+    "expiry_milestone": 73
   },
   {
     "name": "enable-settings-shortcut-search",