Fix bug of unref resources in Lua binding; fd method delete -> cancel.

Signed-off-by: Xiongfei(Alex) Guo <xfguo@credosemi.com>
Fix bug of GC in fd and timeout objects for lua binding.

fd and timeout lua object has a __gc method in its metatable. After the object
is freed and the another new object use the same reference in __uloop_cb and
__uloop_fds, the new object will be freed by the old __gc of the old object
when garbag collecting.

Signed-off-by: Xiongfei(Alex) Guo <xfguo@credosemi.com>