Remove redundant info about DefaultMetricsFactory

The DefaultMetricsFactory was removed from Spring Integration starting
with version 5.4. This commit updates the documentation to match.

See gh-28375

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/spring-integration.adoc

@@ -45,6 +45,3 @@ Spring Boot can also auto-configure an `ClientRSocketConnector` using configurat
 ----
 
 See the {spring-boot-autoconfigure-module-code}/integration/IntegrationAutoConfiguration.java[`IntegrationAutoConfiguration`] and {spring-boot-autoconfigure-module-code}/integration/IntegrationProperties.java[`IntegrationProperties`] classes for more details.
-
-By default, if a Micrometer `meterRegistry` bean is present, Spring Integration metrics will be managed by Micrometer.
-If you wish to use legacy Spring Integration metrics, add a `DefaultMetricsFactory` bean to the application context.