Removed Pipeworks compatibility.

It seems like this chest can not use pipeworks.
When one connect a filter to it and punch or signal the filter it will cause the server to crash.
```
17:27:24: ACTION[ServerThread]: Megaf joins game. List of players: Megaf
17:27:37: ACTION[ServerThread]: Megaf places node pipeworks:filter at (5,7,-17)
17:27:37: ACTION[ServerThread]: facedir: 3
17:27:39: ERROR[main]: ERROR: An unhandled exception occurred: ...minetest/Server/bin/../mods/pipeworks/item_transport.lua:54: bad argument #1 to 'ipairs' (table expected, got nil
)
17:27:39: ERROR[main]: stack traceback:
17:27:39: ERROR[main]:  [C]: in function 'ipairs'
17:27:39: ERROR[main]:  ...minetest/Server/bin/../mods/pipeworks/item_transport.lua:54: in function 'grabAndFire'
17:27:39: ERROR[main]:  ...minetest/Server/bin/../mods/pipeworks/item_transport.lua:150: in function 'punch_filter'
17:27:39: ERROR[main]:  ...minetest/Server/bin/../mods/pipeworks/item_transport.lua:214: in function <...minetest/Server/bin/../mods/pipeworks/item_transport.lua:213>

In thread b693c220:
/home/minetest/Server/src/main.cpp:1955: int main(int, char**): Assertion '0' failed.
Debug stacks:
DEBUG STACK FOR THREAD b23ff440:
#0  virtual void* CurlFetchThread::Thread()
DEBUG STACK FOR THREAD b693c220:
#0  int main(int, char**)
(Leftover data: #1  Dedicated server branch)
(Leftover data: #2  virtual void ServerMap::save(ModifiedState))
(Leftover data: #3  void ItemStack::serialize(std::ostream&) const)
Aborted
```