Polish How-to Customize UserInfo response

Remove unneeded `issuer()` in `ProviderSettings`.

Issue gh-537

docs/src/docs/asciidoc/examples/src/main/java/sample/userinfo/jwt/JwtUserInfoMapperSecurityConfig.java

@@ -183,7 +183,7 @@ public class JwtUserInfoMapperSecurityConfig {
 
 	@Bean
 	public ProviderSettings providerSettings() {
-		return ProviderSettings.builder().issuer("http://localhost:9000").build();
+		return ProviderSettings.builder().build();
 	}
 	// @fold:off