Remove catfile feature flag

533c1948 introduced a new feature flag
on this repository for the catfile cache. However, this flag has been
removed from the Gitaly code base a while ago and is thus void.

This change removes a lingering test referencing this test, as well as
the flags YAML defintion.

config/feature_flags/development/gitaly_catfile-cache.yml

----
-name: gitaly_catfile-cache
-introduced_by_url: 
-rollout_issue_url: 
-milestone: 
-type: development
-group: 
-default_enabled: false

spec/lib/gitlab/gitaly_client_spec.rb

@@ -267,31 +267,25 @@ RSpec.describe Gitlab::GitalyClient do
   end
 
   describe '.request_kwargs' do
-    context 'when catfile-cache feature is enabled' do
-      before do
-        stub_feature_flags('gitaly_catfile-cache': true)
-      end
-
-      it 'sets the gitaly-session-id in the metadata' do
-        results = described_class.request_kwargs('default', timeout: 1)
-        expect(results[:metadata]).to include('gitaly-session-id')
-      end
+    it 'sets the gitaly-session-id in the metadata' do
+      results = described_class.request_kwargs('default', timeout: 1)
+      expect(results[:metadata]).to include('gitaly-session-id')
+    end
 
-      context 'when RequestStore is not enabled' do
-        it 'sets a different gitaly-session-id per request' do
-          gitaly_session_id = described_class.request_kwargs('default', timeout: 1)[:metadata]['gitaly-session-id']
+    context 'when RequestStore is not enabled' do
+      it 'sets a different gitaly-session-id per request' do
+        gitaly_session_id = described_class.request_kwargs('default', timeout: 1)[:metadata]['gitaly-session-id']
 
-          expect(described_class.request_kwargs('default', timeout: 1)[:metadata]['gitaly-session-id']).not_to eq(gitaly_session_id)
-        end
+        expect(described_class.request_kwargs('default', timeout: 1)[:metadata]['gitaly-session-id']).not_to eq(gitaly_session_id)
       end
+    end
 
-      context 'when RequestStore is enabled', :request_store do
-        it 'sets the same gitaly-session-id on every outgoing request metadata' do
-          gitaly_session_id = described_class.request_kwargs('default', timeout: 1)[:metadata]['gitaly-session-id']
+    context 'when RequestStore is enabled', :request_store do
+      it 'sets the same gitaly-session-id on every outgoing request metadata' do
+        gitaly_session_id = described_class.request_kwargs('default', timeout: 1)[:metadata]['gitaly-session-id']
 
-          3.times do
-            expect(described_class.request_kwargs('default', timeout: 1)[:metadata]['gitaly-session-id']).to eq(gitaly_session_id)
-          end
+        3.times do
+          expect(described_class.request_kwargs('default', timeout: 1)[:metadata]['gitaly-session-id']).to eq(gitaly_session_id)
         end
       end
     end