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}