Remove 422 response body logging

The inconsistent structure of these responses was causing mapping
conflicts when these logs were sent to Elasticsearch. Apparently they
are not actively used, so can be removed.

app/controllers/application_controller.rb

@@ -149,10 +149,6 @@ class ApplicationController < ActionController::Base
       payload[:username] = logged_user.try(:username)
     end
 
-    if response.status == 422 && response.body.present? && response.content_type == 'application/json'
-      payload[:response] = response.body
-    end
-
     payload[:queue_duration] = request.env[::Gitlab::Middleware::RailsQueueDuration::GITLAB_RAILS_QUEUE_DURATION_KEY]
   end
 

spec/controllers/application_controller_spec.rb

@@ -530,41 +530,6 @@ describe ApplicationController do
 
       expect(controller.last_payload).to include('correlation_id' => 'new-id')
     end
-
-    context '422 errors' do
-      it 'logs a response with a string' do
-        response = spy(ActionDispatch::Response, status: 422, body: 'Hello world', content_type: 'application/json', cookies: {})
-        allow(controller).to receive(:response).and_return(response)
-        get :index
-
-        expect(controller.last_payload[:response]).to eq('Hello world')
-      end
-
-      it 'logs a response with an array' do
-        body = ['I want', 'my hat back']
-        response = spy(ActionDispatch::Response, status: 422, body: body, content_type: 'application/json', cookies: {})
-        allow(controller).to receive(:response).and_return(response)
-        get :index
-
-        expect(controller.last_payload[:response]).to eq(body)
-      end
-
-      it 'does not log a string with an empty body' do
-        response = spy(ActionDispatch::Response, status: 422, body: nil, content_type: 'application/json', cookies: {})
-        allow(controller).to receive(:response).and_return(response)
-        get :index
-
-        expect(controller.last_payload.has_key?(:response)).to be_falsey
-      end
-
-      it 'does not log an HTML body' do
-        response = spy(ActionDispatch::Response, status: 422, body: 'This is a test', content_type: 'application/html', cookies: {})
-        allow(controller).to receive(:response).and_return(response)
-        get :index
-
-        expect(controller.last_payload.has_key?(:response)).to be_falsey
-      end
-    end
   end
 
   describe '#access_denied' do