Remove 750ms timeout on owners path validation

Summary:
Ref T13164. See PHI748. Path validation has a 750ms timeout which blames to rP5038ab850c, in 2011.

Production path validation is sometimes taking more than 750ms, particularly on the initial page load where we may validate many paths simultaneously.

I have no idea why we have this timeout, and it isn't consistent with how we perform other AJAX requests. Just remove it.

Test Plan:

• Reproduced issue in production, saw all validation calls failing at 750ms. Actual underlying calls succeed, they just take more than 750ms to resolve.
• Loaded path validator locally, got green checkmark.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13164

Differential Revision: https://secure.phabricator.com/D19575