Remove unused CommitsBetween wrapper

In commit ebab4f48 (gitaly_client: Reimplement `#between` via
`#list_commits`, 2021-11-11), we have reimplemented `#between` via
`#list_commits` such that the deprecated CommitsBetween RPC isn't used
in GitLab Rails anymore. What was missed though is that `#between` isn't
being used at all anymore, and all previous callsites had already been
converted to use `#list_commits` in the first place. The calls which
were still visible in Grafana thus weren't caused by Rails, but they
were instead caused by the Elasticsearch indexer.

Remove `#between` altogether given that it's not in use. The feature
flag which has been introduced to convert this wrapper to instead use
`#list_commits` is removed, too.

Changelog: other

config/feature_flags/development/between_commits_via_list_commits.yml

----
-name: between_commits_via_list_commits
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74273
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/345458
-milestone: '14.5'
-type: development
-group: group::gitaly
-default_enabled: false

lib/gitlab/gitaly_client/commit_service.rb

@@ -204,19 +204,6 @@ module Gitlab
         Gitlab::Git::Commit.new(@repository, gitaly_commit)
       end
 
-      def between(from, to)
-        return list_commits(["^" + from, to], reverse: true) if Feature.enabled?(:between_commits_via_list_commits)
-
-        request = Gitaly::CommitsBetweenRequest.new(
-          repository: @gitaly_repo,
-          from: from,
-          to: to
-        )
-
-        response = GitalyClient.call(@repository.storage, :commit_service, :commits_between, request, timeout: GitalyClient.medium_timeout)
-        consume_commits_response(response)
-      end
-
       def diff_stats(left_commit_sha, right_commit_sha)
         request = Gitaly::DiffStatsRequest.new(
           repository: @gitaly_repo,

spec/lib/gitlab/gitaly_client/commit_service_spec.rb

@@ -108,45 +108,6 @@ RSpec.describe Gitlab::GitalyClient::CommitService do
     end
   end
 
-  describe '#between' do
-    let(:from) { 'master' }
-    let(:to) { Gitlab::Git::EMPTY_TREE_ID }
-
-    context 'with between_commits_via_list_commits enabled' do
-      before do
-        stub_feature_flags(between_commits_via_list_commits: true)
-      end
-
-      it 'sends an RPC request' do
-        request = Gitaly::ListCommitsRequest.new(
-          repository: repository_message, revisions: ["^" + from, to], reverse: true
-        )
-
-        expect_any_instance_of(Gitaly::CommitService::Stub).to receive(:list_commits)
-          .with(request, kind_of(Hash)).and_return([])
-
-        described_class.new(repository).between(from, to)
-      end
-    end
-
-    context 'with between_commits_via_list_commits disabled' do
-      before do
-        stub_feature_flags(between_commits_via_list_commits: false)
-      end
-
-      it 'sends an RPC request' do
-        request = Gitaly::CommitsBetweenRequest.new(
-          repository: repository_message, from: from, to: to
-        )
-
-        expect_any_instance_of(Gitaly::CommitService::Stub).to receive(:commits_between)
-          .with(request, kind_of(Hash)).and_return([])
-
-        described_class.new(repository).between(from, to)
-      end
-    end
-  end
-
   describe '#diff_stats' do
     let(:left_commit_id) { 'master' }
     let(:right_commit_id) { 'cfe32cf61b73a0d5e9f13e774abde7ff789b1660' }