Update the successor's Phis in RemoveDeadBlocks

When we remove a dead block, we update its successor's phis (as long
as the successor is still reachable). We can reuse code from
DisconnectAndDelete if we refactor it a little bit.

Bug: 240546614
Fixes: 240546614
Test: art/test/testrunner/testrunner.py --host --64 --optimizing -b
Change-Id: I70c509bd1c9e392118bbf95c7aaac64faa46237f
3 files changed