Remove flag guarding batched computation of changes size

In f73f0c7b (git_access: Use batched new blobs check, 2021-06-21), a
new feature flag had been added to enable batched computation of changes
size in Git authentication checks. With this feature flag enabled, Git
access checks compute all new blobs with a single RPC call instead of
doing one call per changed reference. Given that these RPCs are rather
expensive, this feature flag improves performance when multiple changes
are checked in a context where no quarantine directories are available.

This feature flag has been tested in production since June 22nd, but
couldn't yet be default-enabled because the RPC it relies on has only
been released with v14.1. Given that the feature has been tested for
such a long time now, let's remove its feature flag altogether.

Changelog: performance

config/feature_flags/development/git_access_batched_changes_size.yml

----
-name: git_access_batched_changes_size
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64503
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/334130
-milestone: '14.1'
-type: development
-group: group::gitaly
-default_enabled: false

lib/gitlab/git_access.rb

@@ -498,21 +498,10 @@ module Gitlab
     end
 
     def check_changes_size
-      changes_size =
-        if Feature.enabled?(:git_access_batched_changes_size, project, default_enabled: :yaml)
       revs = ['--not', '--all', '--not']
       revs += changes_list.map { |change| change[:newrev] }
 
-          repository.blobs(revs).sum(&:size)
-        else
-          changes_size = 0
-
-          changes_list.each do |change|
-            changes_size += repository.new_blobs(change[:newrev]).sum(&:size)
-          end
-
-          changes_size
-        end
+      changes_size = repository.blobs(revs).sum(&:size)
 
       check_size_against_limit(changes_size)
     end

spec/lib/gitlab/git_access_snippet_spec.rb

@@ -382,12 +382,11 @@ RSpec.describe Gitlab::GitAccessSnippet do
       it_behaves_like 'a push to repository to make it over the limit'
     end
 
-    shared_examples_for 'a change with GIT_OBJECT_DIRECTORY_RELATIVE env var unset' do
+    context 'a change with GIT_OBJECT_DIRECTORY_RELATIVE env var unset' do
       let(:change_size) { 200 }
 
       before do
-        stub_feature_flags(git_access_batched_changes_size: batched)
-        allow(snippet.repository).to receive(expected_call).and_return(
+        allow(snippet.repository).to receive(:blobs).and_return(
           [double(:blob, size: change_size)]
         )
       end
@@ -396,20 +395,6 @@ RSpec.describe Gitlab::GitAccessSnippet do
       it_behaves_like 'a push to repository below the limit'
       it_behaves_like 'a push to repository to make it over the limit'
     end
-
-    context 'when batched computation is enabled' do
-      let(:batched) { true }
-      let(:expected_call) { :blobs }
-
-      it_behaves_like 'a change with GIT_OBJECT_DIRECTORY_RELATIVE env var unset'
-    end
-
-    context 'when batched computation is disabled' do
-      let(:batched) { false }
-      let(:expected_call) { :new_blobs }
-
-      it_behaves_like 'a change with GIT_OBJECT_DIRECTORY_RELATIVE env var unset'
-    end
   end
 
   describe 'HEAD realignment' do