tests: remove old (and wrong) Hurd workaround

Other than being no more applicable with recent Hurd versions (e.g. 0.5), it was working around a bug in TestTool::init, not properly handling failures in SDL::init.

Basically it reverts commit 4931c49d1dfdc11aaf86d85db734104a37bef538.

It "depends" on the pull request #262.