MAGETWO-31834: Fatal error if trying to navigate to Frontend at first time after install

- Fix unit test

Author: Joan He

lib/internal/Magento/Framework/ObjectManager/Test/Unit/Code/Generator/ConverterTest.php

@@ -80,9 +80,6 @@ public function testGenerate()
             ->method('classLoadable')
             ->will($this->returnValue(true));
 
-        $this->ioObjectMock->expects($this->once())
-            ->method('makeGenerationDirectory')
-            ->will($this->returnValue(true));
         $this->ioObjectMock->expects($this->once())
             ->method('makeResultFileDirectory')
             ->with(self::RESULT_CLASS_NAME)