pkg: remove OpenWSN

pkg/openwsn/Makefile

-PKG_NAME=openwsn
-PKG_URL=https://github.com/openwsn-berkeley/openwsn-fw.git
-PKG_VERSION=ff25e5d0ae5d344ed793a724d60532fb917bf1f8
-PKG_LICENSE=BSD-3-Clause
-
-.PHONY: all
-
-all: git-download
-	"$(MAKE)" -C $(PKG_BUILDDIR)
-
-include $(RIOTBASE)/pkg/pkg.mk

pkg/openwsn/README.md

-# OpenWSN on RIOT
-
-This port of OpenWSN to RIOT is based on current OpenWSN upstream providing a
-BSP with RIOT's interfaces. Currently supported are iotlab-m3 and fox. More
-boards will follow through improvements in netdev radio driver interface.
-
-# Usage
-
-A test can be found in tests/openwsn providing a shell command to initialise
-as root or listening node. And providing a sample Makefile.
-
-Build using
-```Bash
-$> export BOARD=iotlab-m3
-$> export PORT=/dev/ttyTHEPORTOFYOURIOTLAB
-$> make -B clean flash term
-```
-
-To use OpenWSN with RIOT it has to be added to the used packages variable
-```Makefile
-USEPKG += openwsn
-```
-
-On the first build the archive will be fetched, patched and built.
-**WARNING** A call of `make clean` also cleans the OpenWSN tree right now so
-changes to the source code will be lost in the next build.