Remove some redundant set_cheapest() calls.

Remove some redundant set_cheapest() calls.

Commit e2fa76d80 centralized the responsibility for doing
set_cheapest() for a baserel, but these functions added later
seemingly didn't get the memo.  There's no apparent reason why
we need the cheapest path for these relation types to be available
any sooner than it is for other base relation types, so delete the
duplicate calls.  Doesn't save much since there's only one path
in these cases, but it might improve clarity.

Richard Guo

Discussion: https://postgr.es/m/CAMbWs4-KFEU_fDuJPNCOkUu3rwvZvKBEytkd9VrM4kH4-2h1CQ@mail.gmail.com