(bug 50926) Disable feedback via AFTv5 on de.wikipedia

https://gerrit.wikimedia.org/r/#/c/72495/ introduces this variable.

Bug: 50926
Change-Id: Ic5c303013a0ea94c94f42af1bbc2af33c6815741
Merge "(bug 50926) Disable feedback via AFTv5 on de.wikipedia"