Revert "Replace license classifier"

This reverts commit 9406b44657.

Reason for revert:
There is still on-going discussion about the new license expression
and it may be changed in a near future. Until we get more stable
conclusion let's stick with the older format. See [1] to find details.

[1] https://review.opendev.org/c/openstack/nova/+/951226

Change-Id: I7e0ec1df01b9fea9e86d961427a1edc6342f224c

setup.cfg

@@ -3,7 +3,6 @@ name = ironic
 summary = OpenStack Bare Metal Provisioning
 description_file =
     README.rst
-license = Apache-2.0
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/ironic/latest/
@@ -12,6 +11,7 @@ classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
     Intended Audience :: System Administrators
+    License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     Programming Language :: Python
     Programming Language :: Python :: 3 :: Only