remove MoveWrapper from io/async/AsyncUDPServerSocket.h

remove MoveWrapper from io/async/AsyncUDPServerSocket.h

Summary:This is the last place in folly that uses MoveWrapper (other than
the MoveWrapper implementation itself and its tests, of course).

Instead of using a MoveWrapper, the object in question is moved
into the lambda using C++14 syntax, and the lambda is moved in a
call to EventBase::runInEventBaseThread which is possible now
that the EventBase methods accept non-copyable callbacks.

Reviewed By: yfeldblum

Differential Revision: D3169316

fb-gh-sync-id: 2dcb1a523ac417f4619c607898e58b572648e3da
fbshipit-source-id: 2dcb1a523ac417f4619c607898e58b572648e3da