Enable Grape/Gitlab::Json hook

Changelog: performance

config/feature_flags/development/grape_gitlab_json.yml

----
-name: grape_gitlab_json
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/36472
-rollout_issue_url: 
-milestone: '13.2'
-type: development
-group: group::source code
-default_enabled: true

lib/gitlab/json.rb

@@ -180,9 +180,6 @@ module Gitlab
     class GrapeFormatter
       # Convert an object to JSON.
       #
-      # This will default to the built-in Grape formatter if either :oj_json or :grape_gitlab_json
-      # flags are disabled.
-      #
       # The `env` param is ignored because it's not needed in either our formatter or Grape's,
       # but it is passed through for consistency.
       #
@@ -194,11 +191,7 @@ module Gitlab
       def self.call(object, env = nil)
         return object.to_s if object.is_a?(PrecompiledJson)
 
-        if Feature.enabled?(:grape_gitlab_json, default_enabled: true)
-          Gitlab::Json.dump(object)
-        else
-          Grape::Formatter::Json.call(object, env)
-        end
+        Gitlab::Json.dump(object)
       end
     end
 

spec/lib/gitlab/json_spec.rb

@@ -317,36 +317,14 @@ RSpec.describe Gitlab::Json do
     let(:env) { {} }
     let(:result) { "{\"test\":true}" }
 
-    context "grape_gitlab_json flag is enabled" do
-      before do
-        stub_feature_flags(grape_gitlab_json: true)
-      end
-
-      it "generates JSON" do
-        expect(subject).to eq(result)
-      end
-
-      it "uses Gitlab::Json" do
-        expect(Gitlab::Json).to receive(:dump).with(obj)
-
-        subject
-      end
+    it "generates JSON" do
+      expect(subject).to eq(result)
     end
 
-    context "grape_gitlab_json flag is disabled" do
-      before do
-        stub_feature_flags(grape_gitlab_json: false)
-      end
+    it "uses Gitlab::Json" do
+      expect(Gitlab::Json).to receive(:dump).with(obj)
 
-      it "generates JSON" do
-        expect(subject).to eq(result)
-      end
-
-      it "uses Grape::Formatter::Json" do
-        expect(Grape::Formatter::Json).to receive(:call).with(obj, env)
-
-        subject
-      end
+      subject
     end
 
     context "precompiled JSON" do