Revert "Implement CIText as NOCASE alternative in postgresql"

This reverts commit 0f3c1b9d15.

optional/postgresql/conf/queries.sql

@@ -40,10 +40,3 @@ select 1
 create
     database mailu
     owner mailu;
-
--- name: create_citext!
--- Install the CIText extension
-create
-    extension
-    if not exists
-    citext;