Repurpose MacBook Air 11

Reformat SSD, reinstall clean OS, and secure wipe, to prep for repurpose.

...With an SSD drive, Secure Erase and Erasing Free Space are not available in Disk Utility. These options are not needed for an SSD drive because a standard erase makes it difficult to recover data from an SSD. [But it is possible to perform a secure wipe if desired. -rws]