Small refactoring around ExecCreateTableAs().
Since commit
4b74ebf726, the refresh logic is used to populate
materialized views, so we can simplify the error message in
ExecCreateTableAs().
Also, RefreshMatViewByOid() is moved to just after
create_ctas_nodata() call to improve code readability.
Author: Yugo Nagata
Discussion: https://postgr.es/m/
20240802161301.
d975daca9ba7a706fa05ecd7@sraoss.co.jp