Revert "Emergency fix for fleet-server bootstrap issue (#683)" (#695)

Author: mtojek

internal/install/application_configuration_yml.go

@@ -29,6 +29,4 @@ const applicationConfigurationYml = `stack:
 
 const applicationConfigurationYml = `stack:
   image_ref_overrides:
-    8.1.0-SNAPSHOT:
-      # Use stable image versions for Kibana
-      elastic-agent: ` + elasticAgentCompleteImageName + `@sha256:a5c580573376d65ed2eba92d359b411cdae4bf52745af8e3bb8c0c91f8ce53a5`
+`