Remove remnants of AutoTimer support if possible

[wilkinsona]

Much of the AutoTimer support has been removed in favor of the observation support that's been added to WebClient, RestTemplate, and the like. We still have the public org.springframework.boot.actuate.metrics.AutoTimer interface but it's now only used by org.springframework.boot.actuate.metrics.data.MetricsRepositoryMethodInvocationListener. We may be able to remove it in favor of the observation support in Spring Data.

[wilkinsona]

We need to update the documentation based on the outcome of this issue. It shows examples of using @Timed on a @RestController which is no longer supported. We'll either need to remove the section entirely, or update it to use Spring Data Repository examples.

[wilkinsona]

This isn't possible at this time. We'll leave things as they are in Boot 3.0 and migrate to the support that's coming in Spring Data in 3.1. I've opened #33282 to address the documentation around @Timed.