How to disable iPhone requiring backup encyption?

Your iPhone requires you to encrypt your backup?

... and you cannot find how to turn it off? 

iTunes surprised me with the message: "This iPhone requires backup files to be encrypted"

After a lot of digging I have found that this can be caused by installed Profiles (Crashlytics Provisioning Profile in my case, but some other people reported the same with an M1 (the telecommunication company) Profile installed).
To delete it:

1. Go to Settings > General > Profile, tap on the app’s configuration profile.
2. Then tap Delete Profile. If asked, enter your device pass-code, then tap Delete.

Then:

1. Go to the Summary page for your device in iTunes
2. double check "Automatically Back Up" is set to "This computer"
3. double check "Encrypt iPhone backup" is _unchecked_
4. Press "Back Up Now"

Congratulations, your backup will be in:
c:\Users\\AppData\Roaming\Apple Computer\MobileSync\Backup\

Now you can go ahead and get your text messages from it! :)