remove py-schema from repo (already in upstream)

packages/py-schema/package.py

-# Copyright 2013-2022 Lawrence Livermore National Security, LLC and other
-# Spack Project Developers. See the top-level COPYRIGHT file for details.
-#
-# SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
-from spack.package import *
-
-
-class PySchema(PythonPackage):
-    """Simple data validation library"""
-
-    homepage = "https://github.com/keleshev/schema"
-    pypi = "schema/schema-0.7.5.tar.gz"
-
-    version("0.7.5", sha256="f06717112c61895cabc4707752b88716e8420a8819d71404501e114f91043197")
-
-    depends_on("py-setuptools", type="build")
-    depends_on("py-contextlib2@0.5.5:", type=("build", "run"))