Remove unnecessary generator and dead code in AsyncWatchmanTestCase
Remove unnecessary generator and dead code in AsyncWatchmanTestCase

Summary: The task was just to rewrite as a set comprehension, but it leads to another linter warning, so just simplified the expression.

Reviewed By: xavierd

Differential Revision: D25932542

fbshipit-source-id: 7e06fbe4e16819c2491dc93d363d7b140846c625

nodakai/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman