[Notif] Don't use LIVE_REGION_POLITE for pinned-by-user HUNs.

If a promoted notification updates itself every second, using a
LIVE_REGION_POLITE causes the pinned-by-user HUN to queue accessibility
announcements for every second, since the content has changed.

Fixes: 437277095
Bug: 397507681
Flag: EXEMPT BUGFIX
Test: Trigger a notification with a status bar chip then tap chip ->
verify "Notification shade" is announced but the whole notification
content is not announced
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:406194957d323d1837bf1afc615ff652edc552a4
Merged-In: I853500ee55290f6144909d1081fae8d123b45ae8
Change-Id: I853500ee55290f6144909d1081fae8d123b45ae8