Revert "Fix "Could not delete" Exception on removeDirectory"

This reverts commit b8ccfdfd81439f41396ec8d0b28d7f43e7d6a25e.

It is not necessary any longer.

It was a fix for a problem reported in #122.

Which has fixed upstream in composer as it was a problem there.

- https://github.com/magento-hackathon/magento-composer-installer/issues/122
- https://github.com/composer/composer/pull/3158
- https://github.com/composer/composer/pull/3159