doc: Remove mention of natpmp build options

doc/build-openbsd.md

@@ -44,7 +44,7 @@ from ports. However you can build it yourself, [using depends](/depends).
 Refer to [depends/README.md](/depends/README.md) for detailed instructions.
 
 ```bash
-gmake -C depends NO_BOOST=1 NO_LIBEVENT=1 NO_QT=1 NO_SQLITE=1 NO_NATPMP=1 NO_UPNP=1 NO_ZMQ=1 NO_USDT=1
+gmake -C depends NO_BOOST=1 NO_LIBEVENT=1 NO_QT=1 NO_SQLITE=1 NO_UPNP=1 NO_ZMQ=1 NO_USDT=1
 ...
 to: /path/to/bitcoin/depends/*-unknown-openbsd*
 ```