BitmapHandler.php has numerous checks for versions of imagemagick...
The oldest being 6.3.4, which was released in 2007.
We also have 6.5.6 from 2009
And 6.8.9-3 from 2014...
I think we can guarantee we'll have at least those versions...
Jessie has 6.8.9.9-5 - https://packages.debian.org/jessie/imagemagick and PHP had PHP 5...
I think we can basically remove all existing version checks and just assume we have a much newer version (like WMF prod has 6.9.7) based on PHP requirements and therefore what the underlying OS requirement/versions should be