- There was no use of DisallowDeferredHandleDereference, so remove the
  corresponding assertion scope and related code.
- Make DeferredHandleScope::Detach return a unique_ptr rather than a
  raw pointer for clarity.
- Store DeferredHandles in compilation info as unique_ptr rather than
  shared_ptr, as it's never shared.
- Remove some unused methods.

Change-Id: I8327399fd291eba782820dd7a62c3bbdffedac4d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1805645
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63828}