[ios] Remove //ios/intents/* targets and code

They were sample on how to use `generate_intents = true`. This
has now been used by //ios/chrome/widget_kit_extension and the
sample is no longer needed.

Bug: none
Change-Id: I1fb4ca08cd13439707e0665ad09a407ec630f4de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7041742
Reviewed-by: Mark Cogan <marq@chromium.org>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1530122}