Partially revert "GSocket: Fix race conditions on Win32 if multiple threads are waiting on conditions for the same socket"

This partially reverts commit 799f8dcd.
This patch seems to break the writability status of the server socket: once
somebody writes to it with success, then it reports it is not writable
anymore. Also, when the client socket has the flag FD_CONNECT set once,
it is never cleared and then it reports it is always writable, also when
it is not.