Possible incorrect Invitations API prepend for member roles

The following discussion from !134100 (merged) should be addressed:

• @dstull started a discussion:

  @jarka I noticed this today and thought it looked weird.

  Shouldn't we be prepending the Invitations api here instead? Makes me also wonder if not noticed, and it isn't really working, are we really using it anyway?

  API::Invitations.prepend_mod