Add iOS to flag_ownership doc

This CL adds iOS where pertinent to the chrome flag ownership doc.

Bug: 1058614
Change-Id: I6d6af5afb2b3948c59524bde180a9b1a12ac6fb7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2095144
Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748356}

docs/flag_ownership.md

@@ -15,15 +15,12 @@ you find, either:
   the top of the file) and set an appropriate expiration milestone;
 
 - **If it is not in use:** delete it from `kFeatureEntries` in
-  [`chrome/browser/about_flags.cc`](https://cs.chromium.org/chromium/src/chrome/browser/about_flags.cc?sq=package:chromium&g=0&l=1319).
+  [`chrome/browser/about_flags.cc`](https://cs.chromium.org/chromium/src/chrome/browser/about_flags.cc?sq=package:chromium&g=0&l=1319) or 
+  [`ios/chrome/browser/about_flags.mm`](https://cs.chromium.org/chromium/src/ios/chrome/browser/about_flags.mm) for iOS.
   Remember to file a cleanup bug to remove code paths that become dead. It is
   not necessary to delete the corresponding entry in `flag-metadata.json` as it
   will be cleaned up for you in the future.
 
-All existing flags have been set to expire in M76 (~6 months from now). At that
-time, every flag with no owners will be hardcoded to behave as though it was
-always its default value and will be removed from the `chrome://flags` UI.
-
 ## Wait, What Are You Doing?
 
 Presently, Chrome has approximately 600 entries in `chrome://flags`, many of