Revert "[sysdep] Add a sysdep for py-yaml"

This reverts commit aeb128c5.

It exists already in base robotpkg, was a bit blind :)

sysdep/py-yaml.mk

-# robotpkg sysdep/py-yaml.mk
-# Created:			Arnaud Degroote on Mon,  1 Sep 2014
-#
-DEPEND_DEPTH:=		${DEPEND_DEPTH}+
-PY_YAML_DEPEND_MK:=	${PY_YAML_DEPEND_MK}+
-
-ifeq (+,$(DEPEND_DEPTH))
-DEPEND_PKG+=		py-yaml
-endif
-
-ifeq (+,$(PY_YAML_DEPEND_MK)) # --------------------------------------------
-
-PREFER.py-yaml?=	system
-
-DEPEND_USE+=		py-yaml
-
-DEPEND_ABI.py-yaml?=	${PKGTAG.python}-yaml>=3.0
-
-SYSTEM_SEARCH.py-yaml=\
-  '${PYTHON_SYSLIBSEARCH}/yaml/__init__.py'
-
-SYSTEM_PKG.Debian.py-yaml=	python-yaml (python-${PYTHON_VERSION})
-SYSTEM_PKG.Fedora.py-yaml=	PyYAML 
-SYSTEM_PKG.NetBSD.py-yaml=	textproc/${PKGTAG.python}-yaml
-SYSTEM_PKG.Ubuntu.py-yaml=	python-yaml (python-${PYTHON_VERSION})
-SYSTEM_PKG.Gentoo.py-yaml=	dev-python/pyyaml (python-${PYTHON_VERSION})
-
-include ../../mk/sysdep/python.mk
-
-export YAMLTESTS=	$(word 1,${SYSTEM_FILES.py-yaml})
-
-endif # PY_YAML_DEPEND_MK --------------------------------------------------
-
-DEPEND_DEPTH:=		${DEPEND_DEPTH:+=}