Remove outdated GitLab version references

Remove outdated GitLab version references

doc/api/version.md

@@ -6,8 +6,6 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Version API **(FREE)**
 
-> Introduced in GitLab 8.13.
-
 Retrieve version information for this GitLab instance. Responds `200 OK` for
 authenticated users.
 

doc/integration/akismet.md

@@ -16,8 +16,7 @@ Admin page.
 Privacy note: GitLab submits the user's IP and user agent to Akismet.
 
 NOTE:
-In GitLab 8.11 and later, all issues are submitted to Akismet.
-In earlier GitLab versions, this only applied to API and non-project members.
+GitLab submits all issues to Akismet.
 
 Akismet configuration is available to users on self-managed GitLab. Akismet is already enabled on
 GitLab SaaS (GitLab.com), where it's configuration and management are handled by GitLab Inc.

doc/user/project/integrations/slack_slash_commands.md

@@ -6,8 +6,6 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Slack slash commands **(FREE SELF)**
 
-> Introduced in GitLab 8.15.
-
 If you want to control and view GitLab content while you're
 working in Slack, you can use Slack slash commands.
 To use Slack slash commands, you must configure both Slack and GitLab.