Task posting v3: manual changes in zlib to continue handle refactors

This change is part of a mass refactor, with no user-facing changes.

Remove references to task runner handles, and remove all calls,
includes, and instantiations of thread and sequenced task runner handles

these were replaced with references to the new api:
TaskRunner::CurrentDefaultHandle and associated methods.

Bug: 1026641
Change-Id: I10de62bd0e18379730d216aa94dcff5090c29ea9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4133656


Reviewed-by: Chris Blume <cblume@chromium.org>
Commit-Queue: Sean Maher <spvw@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1090870}
NOKEYCHECK=True
GitOrigin-RevId: f37ab4771fbb8ae0e6b6440c792391e03140a553