Remove `migrating-1.3` from the Guide for 1.4.
Remove `migrating-1.3` from the Guide for 1.4.

It's still in the Guide for 1.3, but it seems unnecessary to have it
here as well.

Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor