remove redundant check from find_affected_books
remove redundant check from find_affected_books

The current code checks first if cfg.CONF.only_book is _not_ defined
and immediately after that, whether cfg.CONF.only_book _is_ defined
before it uses that list.

This patch removes the second, redundant check.

Change-Id: I701f530efff9c13b098d9f9b974c8d0eb6aabcb7

savinash47/openstack-doc-tools,openstack/openstack-doc-tools,savinash47/openstack-doc-tools,savinash47/openstack-doc-tools,openstack/openstack-doc-tools