Fully remove the successor blocks when effect-control-linearization
reaches an unreachable node and is maintaining the schedule. Previously
we just updated the current_block_'s successor and removed any
unreachable predecessors from end, however if the current_block_ is not
an original block in the schedule, but a new one added due to control
flow from effect control linearization lowering, the removed successor
blocks could still be re-connected to the end block when they were
lowered. Instead, entirely remove these unreachable blocks from the
predecessor / successor chains, and have the effect-control-linearizer
avoid lowering these blocks entirely.

BUG=chromium:1076569,v8:9684

Change-Id: I4b4216019d55aef5363d88255726b85df8e7ada5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2179842Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67595}