Remove deprecation note for APM Server standalone

[simitt]

Starting ECK with a standalone APM Server issues a warning that it is deprecated from 8.0.0 onwards. The standalone server has not actually been deprecated yet. We should remove this deprecation note to avoid user confusion.

[ebuildy]

Well, they call it "legacy" since v7:

https://www.elastic.co/guide/en/apm/guide/current/legacy-apm-overview.html

[simitt]

The focus shifted towards the Elastic Agent managed APM Server, but the standalone server has not been deprecated, therefore the deprecation warning should be removed. We are aware that the usage of the term "legacy" is not ideal here.

[ebuildy]

Ho I see, this is very hard to understand, also from legacy APM documentation at https://www.elastic.co/guide/en/apm/guide/current/legacy-apm-overview.html:

This method of installing APM Server will be **deprecated** and removed in a future release. Please consider getting started with the [Elastic APM integration](https://www.elastic.co/guide/en/apm/guide/current/apm-quick-start.html) instead.

I'm afraid that the products are getting more and more complicated (here a screenshot of the k8s secrets created by the operator when deploying the legacy APM server):

I had to install on kibana the APM integration to make this working, whereas before, the setup was straightaway