[8.6](backport #3752) docs: remove false deprecation note for standal…

…one apm-server (#3767)

* docs: remove false deprecation note for standalone apm-server (#3752)

(cherry picked from commit 38f04c9)

# Conflicts:
#	docs/en/apm-server/upgrading-to-8.x.asciidoc

* Update docs/en/apm-server/upgrading-to-8.x.asciidoc

---------

Co-authored-by: kruskall <99559985+kruskall@users.noreply.github.com>
Co-authored-by: Brandon Morelli <brandon.morelli@elastic.co>

docs/en/apm-server/upgrading-to-8.x.asciidoc

@@ -29,8 +29,7 @@ See the APM <<release-notes,release notes>>, <<apm-breaking,breaking changes>> f
 Starting in version 7.14, there are two ways to run Elastic APM.
 Determine which method you're using, then use the links below to find the correct upgrading guide.
 
-* **Standalone (legacy)**: Users in this mode run and configure the APM Server binary.
-This mode has been deprecated and will be removed in a future release.
+* **Standalone**: Users in this mode run and configure the APM Server binary.
 * **{fleet} and the APM integration**: Users in this mode run and configure {fleet} and the Elastic APM integration.
 
 **Self-installation (non-{ecloud} users) upgrade guides**