[Notif redesign] Remove negative margin layout from convo/call HUNs

Negative margins are generally not recommended, and if we tweak the
margins of the other children here a little bit we can align the actions
just fine without needing a negative margin.

Bug: 378660052
Test: manual + screenshot tests
Flag: android.app.notifications_redesign_templates
Change-Id: I58f2cf80eed5c9ce28320134acc8e834cce55684