[Flags] Extend flags for ongoing autofill experiments

The experiments for label disambiguation and substring matching autofill
suggestions are still ongoing. Therefore, update owners and extend the
expiry milestone.

Bug: None
Change-Id: I61dfbaf0b281e71dd6c0a6e908ddf2677047bcfd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1868992Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Friedrich [CET] <fhorschig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707312}

chrome/browser/flag-metadata.json

@@ -332,13 +332,13 @@
   },
   {
     "name": "autofill-use-improved-label-disambiguation",
-    "owners": [ "ftirelo", "tmartino" ],
-    "expiry_milestone": 77
+    "owners": [ "fhorschig" ],
+    "expiry_milestone": 81
   },
   {
     "name": "autofill-use-mobile-label-disambiguation",
-    "owners": [ "ftirelo", "tmartino" ],
-    "expiry_milestone": 79
+    "owners": [ "fhorschig" ],
+    "expiry_milestone": 81
   },
   {
     "name": "back-forward-cache",
@@ -1741,8 +1741,8 @@
   },
   {
     "name": "enable-suggestions-with-substring-match",
-    "owners": [ "tmartino" ],
-    "expiry_milestone": 77
+    "owners": [ "fhorschig" ],
+    "expiry_milestone": 81
   },
   {
     "name": "enable-surfacecontrol",