Issue #3260766 by andypost: Remove deprecated file.inc and its mentions

core/includes/file.inc

core/includes/install.core.inc

core/includes/theme.maintenance.inc

core/lib/Drupal/Core/DrupalKernel.php

core/lib/Drupal/Core/Form/FormBuilder.php

core/lib/Drupal/Core/Render/Element/File.php

core/lib/Drupal/Core/Test/TestRunnerKernel.php

core/modules/file/file.api.php

...rupal/KernelTests/Core/File/FileSystemDeprecationTest.php

core/tests/Drupal/KernelTests/Core/File/FileTestBase.php

core/tests/Drupal/KernelTests/Core/File/NameMungingTest.php