Reverts #2995 (#3108) (#3109)

With this commit we revert the migration instructions to version 8.9.0 for Universal Profiling. There were some edge cases that we did not anticipate and therefore we fallback to the prior upgrade procedure of requiring users to wipe data for the upgrade.

(cherry picked from commit 2206052)

Co-authored-by: Daniel Mitterdorfer <danielmitterdorfer@users.noreply.github.com>

docs/en/observability/index.asciidoc

@@ -170,8 +170,6 @@ include::profiling-use-a-proxy.asciidoc[leveloffset=+3]
 include::profiling-probabilistic-profiling.asciidoc[leveloffset=+3]
 
 include::profiling-upgrade.asciidoc[leveloffset=+2]
-include::profiling-upgrade-fresh.asciidoc[leveloffset=+3]
-include::profiling-upgrade-migrate.asciidoc[leveloffset=+3]
 
 include::profiling-troubleshooting.asciidoc[leveloffset=+2]
 

docs/en/observability/profiling-get-started.asciidoc

@@ -83,9 +83,12 @@ NOTE: To configure data ingestion, you need elevated privileges, typically the `
 
 If you're upgrading from a previous version with Universal Profiling enabled, see the <<profiling-upgrade,upgrade guide>>.
 
-[discrete]
-[[profiling-install-host-agent]]
-== Install the host-agent
+IMPORTANT: When upgrading, you must remove all existing profiling data.
+We still recommend upgrading as the latest version contains several improvements and new features.
+
+[discrete] 
+[[profiling-install-host-agent]] 
+== Install the host-agent 
 You have the following options when installing the host-agent:
 
 . <<profiling-install-host-agent-standalone, Install the host-agent in standalone mode>>
@@ -112,12 +115,12 @@ image::images/profiling-k8s-hostagent.png[]
 
 To install the host-agent using the {agent} and the Universal Profiling Agent integration, complete the following steps:
 
-. Copy the `secret token` and `Universal Profiling Collector url` from the Elastic Agent Integration
+. Copy the `secret token` and `Universal Profiling Collector url` from the Elastic Agent Integration 
 +
 [role="screenshot"]
 image::images/profiling-elastic-agent.png[]
 +
-. Click `Manage Universal Profiling Agent in Fleet` to complete the integration.
+. Click `Manage Universal Profiling Agent in Fleet` to complete the integration. 
 . On the Integrations page, click **Add Universal Profiling Agent**.
 . In **Universal Profiling Agent → Settings**, add the information you copied from the *Add profiling data* page:
 .. Add the Universal Profiling collector URL to the **Universal Profiling collector endpoint** field.