Drop DISABLE_PUMA_NAKAYOSHI_FORK from Puma config

Puma 6 dropped support for nakayoshi_fork
(puma/puma#2258). GitLab has been running
Puma 6 since GitLab 16.1
(https://gitlab.com/gitlab-org/gitlab/-/merge_requests/119135).

Changelog: changed

Author: stanhu

files/gitlab-cookbooks/gitlab/templates/default/puma.rb.erb

@@ -112,13 +112,6 @@ worker_timeout <%= @worker_timeout %>
 # https://github.com/puma/puma/blob/master/5.0-Upgrade.md#lower-latency-better-throughput
 wait_for_less_busy_worker ENV.fetch('PUMA_WAIT_FOR_LESS_BUSY_WORKER', 0.001).to_f
 
-# nakayoshi_fork was removed in Puma 6.0: https://github.com/puma/puma/issues/2258
-# https://github.com/puma/puma/blob/master/5.0-Upgrade.md#nakayoshi_fork
-if Gem::Version.new(Puma::Const::PUMA_VERSION).canonical_segments.first == 5 &&
-     ENV['DISABLE_PUMA_NAKAYOSHI_FORK'] != 'true'
-  nakayoshi_fork
-end
-
 # Use customised JSON formatter for Puma log
 require_relative "<%= @install_dir %>/embedded/service/gitlab-rails/lib/gitlab/puma_logging/json_formatter"