Remove redundant runner version upgrade alert

What does this MR do and why?

☝ Depends on !132636 (merged). Implements #423770 (closed).

This change removes the version upgrade alert at the top of outdated runners details.

The same information is already contained in the runner version information. The badge that warns users contains the same information.

Changelog: changed
EE: true

Screenshots or screen recordings

Before	After

How to set up and validate locally

Unless you have some outdated runners, it may be hard to downgrade your runners. We can simply change the data to force a change:

1. While running GitLab Ultimate license
2. Edit the following file to return either :available or :recommended as upgrade status

diff --git a/ee/app/graphql/ee/types/ci/runner_type.rb b/ee/app/graphql/ee/types/ci/runner_type.rb
index 34757f57f97d..a9afea1e7321 100644
--- a/ee/app/graphql/ee/types/ci/runner_type.rb
+++ b/ee/app/graphql/ee/types/ci/runner_type.rb
@@ -25,6 +25,7 @@ module RunnerType
             alpha: { milestone: '14.10' }
 
           def upgrade_status
+            return :available
             return unless upgrade_status_available?
 
             BatchLoader::GraphQL.for(object.id).batch(key: :upgrade_status) do |runner_ids, loader|

1. Log in as admin
2. Visit the Admin -> Runners page (http://gdk.test:3000/admin/runners/)
3. Pick any runner to see it's details by clicking on the runner name
4. Confirm the alter is not there, as the badge contains the required information

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #423770 (closed)