ccfbd92 has replaced all existing in-core callers of this function in
favor of durable_rename(). durable_rename_excl() is by nature unsafe on
crashes happening at the wrong time, so just remove it.
Author: Nathan Bossart
Reviewed-by: Robert Haas, Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/20220407182954.GA1231544@nathanxps13