More drop of non-obsoleted aggregate signatures removed

git-svn-id: http://svn.osgeo.org/postgis/trunk@12254 b70326c6-7e19-0410-871a-916f4a2858ee
Allow DROP (with no IF EXISTS) to end up in upgrade scripts

Fixes raster upgrade

git-svn-id: http://svn.osgeo.org/postgis/trunk@12255 b70326c6-7e19-0410-871a-916f4a2858ee