I read section 7 of AGPLv3 quite differently from OnlyOffice: it clearly calls it "Additional Permissions" throughout, and also says this:

  When you convey a copy of a covered work, you may at your option remove any additional permissions from that copy, or from any part of it.
  ...
  All other non-permissive additional terms are considered "further restrictions" within the meaning of section 10. If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term.