Change from using CTE to use subquery so results are the same across all platforms
reason necessary in PostgreSQL 12, CTE changed from being always materialized to being often inlined.  
This means PG12, no longer behaves like old CTE and behaves more like subquery.
As a result 12 CTE is outputting 4 warnings instead of 1 like older versions. 
Changing to just subquery should force all to output 4 warnings.
references #4329 for PostGIS 3.0

git-svn-id: http://svn.osgeo.org/postgis/trunk@17268 b70326c6-7e19-0410-871a-916f4a2858ee