Show reject hint text for all incoming calls

The function setHintText sets the hint text reject text to null when
hintText for answering a call is non-null.

Correcting so the reject text is always be set to
call_incoming_swipe_to_reject regardless of the value of hintText.

This is an upstream change from:
https://android-review.googlesource.com/c/platform/packages/apps/Dialer/+/612667

Bug: 73018780
Test: manual
PiperOrigin-RevId: 185020322
Change-Id: I413f8cf63a1b11e70300536a13c1a8a103d847cc