Remove unused arguments from pg_replication_origin_xact_reset function.

Remove unused arguments from pg_replication_origin_xact_reset function.

The document specifies that pg_replication_origin_xact_reset function
doesn't have any argument variables. But previously it was actually
defined so as to have two argument variables, though they were not
used at all. That is, the pg_proc entry for that function was incorrect.
This patch fixes the pg_proc entry and removes those two arguments
from the function definition.

No back-patch because this change needs a catalog version bump
although the issue exists in 9.5 as well. Instead, a note about those
unused argument variables will be added to 9.5 document later.

Catalog version bumped due to the change of pg_proc.