A dedicated Msg3 TDA is simply not necessary: get_feasible_msg3_tda()
already iterates through all TDAs to find a suitable one for Msg3, and
takes things such as parameter Δ already into account.
The only prerequisite is that the ra_ResponseWindow is long enough. In
some configurations, Msg3 TDA ensured that Msg2 still happened during
ra_ResponseWindow, while Msg3 was outside of it. This is not necessarily
the case anymore, unless ra_ResponseWindow is long enough.
For the normal user, removing ra_ResponseWindow from the config will be
enough.