Revert of [inspector] avoid cloning of async call chains (patchset #7 id:120001 of https://codereview.chromium.org/2816043006/ )

Reason for revert:
Speculative revert. Seems to block the roll:
https://codereview.chromium.org/2822983004/

Might require changing a browser test first?

Original issue's description:
> [inspector] avoid cloning of async call chains
>
> - separated V8StackTraceImpl and AsyncStackTrace,
> - V8Debugger owns all AsyncStackTrace and cleanup half of them when limit is reached (first created - first cleaned),
> - V8StackTraceImpl, AsyncStackTrace and async-task-related tables in V8Debugger have weak reference to other async stack traces.
> - async tasks are cleared with related async stacks.
>
> BUG=v8:6189
> R=dgozman@chromium.org
>
> Review-Url: https://codereview.chromium.org/2816043006
> Cr-Commit-Position: refs/heads/master@{#44670}
> Committed: https://chromium.googlesource.com/v8/v8/+/1bca73bc832c645138bd3e0306fcaa8bb44dad04

TBR=dgozman@chromium.org,kozyatinskiy@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:6189

Review-Url: https://codereview.chromium.org/2825713002
Cr-Commit-Position: refs/heads/master@{#44678}