Sync declarations and definitions of two new tablecmds.c functions.

Sync declarations and definitions of two new tablecmds.c functions.

Buildfarm member drongo complained because the definitions of these
functions used "const Oid foo" where the forward declarations just
had "Oid foo".  (I'm a bit surprised that drongo seems to be the only
complainant.)  I chose to fix this by removing the "consts" because
(a) I'm generally not a fan of using const that way, and (b) it was
a minority usage even within these two functions, let alone compared
to the rest of our code base.

Oversight in commit eec0040c4, so no need for back-patch.