set timeout to 0 for watchman find queries

Summary: We were using a 10-second timeout for watchman find queries. There's been no reason to do that ever since we got cookie files.

Test Plan: `arc unit --everything` on Linux. @wez, want to test it out on the other OSes we support?

Reviewers: wez

Reviewed By: wez

Differential Revision: https://phabricator.fb.com/D918249

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extra : rebase_source : 7e6149a7a009a84b5627ba77ab5cef0df0829b39
extra : amend_source : 31ea2f5f1c021f5e9ca883dd557249012dd3d779