Remove 3.7

> 3.7 goes out of any kind of support on October 1st. There will be one more security patch release of 3.7.x, after that, we can basically assume the 3.7 flavour of this image won't have any upstream releases to benefit from.

> Honestly, the attack 3.7.28 will address is local, requires elevated privileges and is Windows-specific. So this image isn't really affected.

- Michael Klishin

Author: tianon