Remove seven OSX 10.6 from CI

Seven osx 10.6 has been removed from CI capasity. Free capasity will
be used for OSX 10.9. Ten OSX 10.6 mini's will stay on CI

Change-Id: Ibab66922f91feb741af9c07b21f371e3ef305718
Reviewed-by: Simo Fält <simo.falt@digia.com>