[Flag] Extend enable-experimental-kernel-vm-support flag

We will need this flag until we have completed the uprev of SKL-Y and
SKL-U Chrome OS systems to their new kernels.  It's unclear exactly when
this will be done, but my best guess right now is around M87.

Also, remove Jon from the flag contacts as he's moved on to other
adventures.

BUG=b:144308685

Change-Id: I7675b7542b8f73a82f958bb50dfc9bd64a91486a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1991723Reviewed-by: David Munro <davidmunro@google.com>
Commit-Queue: Ross Zwisler <zwisler@google.com>
Auto-Submit: Ross Zwisler <zwisler@google.com>
Cr-Commit-Position: refs/heads/master@{#729576}

chrome/browser/flag-metadata.json

@@ -1336,8 +1336,8 @@
   },
   {
     "name": "enable-experimental-kernel-vm-support",
-    "owners": [ "jflat", "zwisler" ],
-    "expiry_milestone": 82
+    "owners": [ "zwisler" ],
+    "expiry_milestone": 87
   },
   {
     "name": "enable-experimental-productivity-features",