Rely on obsah to pull in Ansible

obsah already pulls in either ansible or ansible-core, depending on the
Python version. There's no need for obal itself to pull it in.

setup.py

@@ -61,7 +61,7 @@ def find_package_data(package, data_dir):
 
     packages=find_packages(exclude=['contrib', 'docs', 'tests']),
 
-    install_requires=['ansible >= 2.5', 'obsah >= 0.0.3'],
+    install_requires=['obsah >= 0.0.3'],
 
     extras_require={
         'argcomplete': ['argcomplete'],