ergm::remove.offset.formula() has been deprecated in favour of statnet.common::filter_rhs.formula().

[krivit]

I am doing some reverse dependency checks in preparation for ergm 3.11 release, and it looks like btergm is still importing ergm::remove.offset.formula() despite it having been deprecated over a year ago. (The code that uses it does not appear to be tested by R CMD check.) Please use statnet.common::filter_rhs.formula() instead.