Reland "Clean up exported PRs after chromium CLs are abandoned"

This reverts commit 332ffa60.

Reason for revert: <This is actually a false alarm. When we close upstream PRs, we have checked there is no exportable change in the chromium CL.>

Original change's description:
> Revert "Clean up exported PRs after chromium CLs are abandoned"
>
> This reverts commit f7be15f9.
>
> Reason for revert: <There is a chance we will always close exported PR instead of merging it when chromium CL is merged. Revert for now.>
>
> Original change's description:
> > Clean up exported PRs after chromium CLs are abandoned
> >
> > We now run this as a step in wpt exporter. After a chromium CL
> > has been abandoned for more than two weeks, the exported PR will
> > be closed automatically.
> >
> > Merged CL with no exportable changes will cause a previously exported
> > Pr to be closed immediately.
> >
> > Bug: 1034348
> > Change-Id: I835acb1ef98f5eab0fd9776eb99da13533ff1c47
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4049884


> > Auto-Submit: Weizhong Xia <weizhong@google.com>
> > Reviewed-by: Jonathan Lee <jonathanjlee@google.com>
> > Commit-Queue: Weizhong Xia <weizhong@google.com>
> > Cr-Commit-Position: refs/heads/main@{#1075423}
>
> Bug: 1034348
> Change-Id: I1576ab533b6b1507cce02de801a3ce87cb0f3466
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4055450
> Commit-Queue: Weizhong Xia <weizhong@google.com>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Cr-Commit-Position: refs/heads/main@{#1075571}

Bug: 1034348
Change-Id: Ib7e81a68dc3012581e8ca8e77000c58d5e73273f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4061867


Reviewed-by: Jonathan Lee <jonathanjlee@google.com>
Commit-Queue: Weizhong Xia <weizhong@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Weizhong Xia <weizhong@google.com>
Cr-Commit-Position: refs/heads/main@{#1076327}