docs: Removed suggestion to use deprecated API

IntentService is deprecated, and had suggested devs use WorkManager or JobIntentService instead, but IntentService is now deprecated too. Per communication with WorkManager owner, just deleted the reference to JobIntentService.

Per Bart, it's okay to submit docs-only changes to tm-dev so they go live before the U preview.

Change-Id: I57aacc8f55f93edf0a1d76bf6fa3fc73974a50af
Test: [go/abtd docs build]
Bug: 256197684