Fix/Simplify the atomic.wait/nofity implementations (#2044)

Use the shared memory's shared_mem_lock to lock the whole atomic.wait and
atomic.notify processes, and use it for os_cond_reltimedwait and os_cond_notify,
so as to make the whole processes actual atomic operations:
the original implementation accesses the wait address with shared_mem_lock
and uses wait_node->wait_lock for os_cond_reltimedwait, which is not an atomic
operation.

And remove the unnecessary wait_map_lock and wait_lock, since the whole
processes are already locked by shared_mem_lock.

Author: wenyongh