The replication origin code was using inconsistent naming
conventions. Functions were typically prefixed with 'replorigin',
while typedefs and constants used "RepOrigin".
This commit unifies the naming convention by renaming RepOriginId to
ReplOriginId.
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CAD21AoBDgm3hDqUZ+nqu=ViHmkCnJBuJyaxG_yvv27BAi2zBmQ@mail.gmail.com