This reverts commit 66b2536ea0.
I misunderstood commit ac56a5c2a0
and caused a FD leak when pid locking is not used.
A LockHandle contains an action that will close the underlying lock
file, and that action is run when it is closed. In the case of a shared
lock, the lock file is opened once for each LockHandle, and only
the one for the LockHandle that is being closed will be closed.