Remove header_read_timeout_buffered_io featureflag

The feature flag has been default enabled with:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/81910

Changelog: other

config/feature_flags/development/header_read_timeout_buffered_io.yml

----
-name: header_read_timeout_buffered_io
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/78065
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/350233
-milestone: '14.8'
-type: development
-group: group::integrations
-default_enabled: true

lib/gitlab/http_connection_adapter.rb

@@ -29,17 +29,13 @@ module Gitlab
       http = super
       http.hostname_override = hostname if hostname
 
-      if Feature.enabled?(:header_read_timeout_buffered_io, default_enabled: :yaml)
-        gitlab_http = Gitlab::NetHttpAdapter.new(http.address, http.port)
+      gitlab_http = Gitlab::NetHttpAdapter.new(http.address, http.port)
 
-        http.instance_variables.each do |variable|
-          gitlab_http.instance_variable_set(variable, http.instance_variable_get(variable))
-        end
-
-        return gitlab_http
+      http.instance_variables.each do |variable|
+        gitlab_http.instance_variable_set(variable, http.instance_variable_get(variable))
       end
 
-      http
+      gitlab_http
     end
 
     private

spec/lib/gitlab/http_connection_adapter_spec.rb

@@ -27,16 +27,6 @@ RSpec.describe Gitlab::HTTPConnectionAdapter do
       end
     end
 
-    context 'with header_read_timeout_buffered_io feature disabled' do
-      before do
-        stub_feature_flags(header_read_timeout_buffered_io: false)
-      end
-
-      it 'uses the regular Net::HTTP class' do
-        expect(connection).to be_a(Net::HTTP)
-      end
-    end
-
     context 'when local requests are allowed' do
       let(:options) { { allow_local_requests: true } }