Disable priority conversation widget for secondary users

Test: NotificationConversationInfoTest.java
Test: make a conversation priority on the primary user
Test: make a conversation priority on a secondary user
Bug: 288896269
(cherry picked from commit adf62031)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:95659d74cfa1f6d7a9796b5d595c99df253ec054)
Merged-In: I3f3991d2cb7fb9970cc8ada39ceae9a7ff2fcb31
Change-Id: I3f3991d2cb7fb9970cc8ada39ceae9a7ff2fcb31