Use proper public API for OC_Helper::getFileNameMimeType

apps/files_sharing/api/local.php

apps/files_trashbin/ajax/preview.php

apps/files_trashbin/lib/helper.php

apps/files_versions/ajax/preview.php

lib/private/files/objectstore/objectstorestorage.php

lib/private/files/storage/common.php

lib/private/helper.php

tests/lib/helper.php