ios: Update build instructions

* Remove references to how things worked before Xcode 9, which was
  released in 2017.
* Remove references to the Chromium IRC channel, which was shut down in
  2021. Direct people to Slack and the mailing lists instead.

Change-Id: Iaf019ef8d38950f44690aced900c8b4aea7ffc63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6565543
Reviewed-by: Sylvain Defresne <[email protected]>
Commit-Queue: Sylvain Defresne <[email protected]>
Auto-Submit: Raphael Kubo da Costa <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1462668}
diff --git a/docs/ios/build_instructions.md b/docs/ios/build_instructions.md
index f667e929..3cfed37 100644
--- a/docs/ios/build_instructions.md
+++ b/docs/ios/build_instructions.md
@@ -324,9 +324,8 @@
 $ out/Debug-iphonesimulator/iossim -i out/Debug-iphonesimulator/Chromium.app
 ```
 
-From Xcode 9 on, `iossim` no longer automatically launches the Simulator. This must now
-be done manually from within Xcode (`Xcode > Open Developer Tool > Simulator`), and
-also must be done *after* running `iossim`.
+Note that `iossim` does not automatically launch the Simulator. This must be
+done manually *after* running `iossim`.
 
 ### Passing arguments
 
@@ -434,10 +433,9 @@
 files; instead see the procedures for [working with
 files](working_with_files.md).
 
-If you have problems building, join us in `#chromium` on `irc.freenode.net` and
-ask there. As mentioned above, be sure that the
-[waterfall](https://build.chromium.org/buildbot/waterfall/) is green and the tree
-is open before checking out. This will increase your chances of success.
+If you have problems building, you can join us on
+[Slack](https://www.chromium.org/developers/slack/) or one of our [mailing
+lists](https://www.chromium.org/developers/technical-discussion-groups/).
 
 ### Debugging