[CLIENT] Remove the tests for "found"/"exists" in the integration test

This change reflects the background-incompatible change from
elastic/elasticsearch#4480

Related: d540aa6

test/integration/client_test.rb

@@ -36,12 +36,11 @@ class Elasticsearch::Transport::ClientIntegrationTest < Elasticsearch::Test::Int
       @client.perform_request 'GET', '_cluster/health?wait_for_status=green', {}
 
       response = @client.perform_request 'GET', 'myindex/mydoc/1?routing=XYZ'
-      assert_equal true, response.body['found']
+      assert_equal 200, response.status
       assert_equal 'bar', response.body['_source']['foo']
+
       assert_raise Elasticsearch::Transport::Transport::Errors::NotFound do
-        response = @client.perform_request 'GET', 'myindex/mydoc/1?routing=ABC'
-        assert_nil response.body['_source']
-        assert_equal false, response.body['found']
+        @client.perform_request 'GET', 'myindex/mydoc/1?routing=ABC'
       end
     end