Slightly simplified an example.

Removed superfluous `@Autowired` and made the constructor package private.

Closes #1072

src/main/asciidoc/jdbc.adoc

@@ -963,8 +963,7 @@ public class UserManagementImpl implements UserManagement {
   private final UserRepository userRepository;
   private final RoleRepository roleRepository;
 
-  @Autowired
-  public UserManagementImpl(UserRepository userRepository,
+  UserManagementImpl(UserRepository userRepository,
     RoleRepository roleRepository) {
     this.userRepository = userRepository;
     this.roleRepository = roleRepository;