Omit extra nginx enablement in ref arch

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Nginx is enabled by default (based on code and testing) in reference architecture for Rails servers, no need to manually enable it

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doc/administration/reference_architectures/10k_users.md

@@ -1953,7 +1953,6 @@ On each node perform the following:
    ## Disable components that will not be on the GitLab application server
    roles(['application_role'])
    gitaly['enable'] = false
-   nginx['enable'] = true
    sidekiq['enable'] = false
 
    ## PostgreSQL connection details