mail/fetchmail: Chase src 0aa2700123e2: Put OPIE to rest

As of src 0aa2700123e2 OPIE has been removed from 14-CURRENT. When
building on a 14-CURRENT machine with __FreeBSD_version > 1400071
avoid linking libopie else this will result a build failure or if
built the following runtime error:

ld-elf.so.1: Shared object "libopie.so.8" not found, required by "fetchmail"