remove bogus file permissions, re #367 (and others)

db/migrations/1.296_biest_10803_fix.php

db/migrations/1.326_courseware_integration.php

db/migrations/1.328_resize_oer_content_type_length.php

db/migrations/5.1.17_add_courseware_templates.php

db/migrations/5.1.18_add_courseware_tasks.php

...s/5.1.19_add_courseware_structural_element_discussion.php