Remove the do_close parameter from stop_watching_dir

Summary:
Depends on D903726.

`do_close` is unused.

Test Plan: Inspecting the code, and running `arc unit --everything`.

Reviewers: wez

Reviewed By: wez

Differential Revision: https://phabricator.fb.com/D903833

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extra : rebase_source : d86bf0cd313ee7419357a730ada67b81bd93f40b
extra : amend_source : e79e8fe63e8e5ec34cabc6f79fae4f219a024bd4