fix: remove 'public' schema from __words table in fix_version_3_tables

If you are using a different schema than public, fix_version_3_tables
crashes on the migration/setup.

Nothing else n the postgresql code uses an explicit public schema.

This removes an impediment for those wanting to use schemas rather
than databases as the primary organizational structure.

See: issue2551299

Also see: issue2550852 for code to allow use of schemas as a first
class config parameter.

roundup/backends/back_postgresql.py

@@ -381,7 +381,7 @@ def fix_version_2_tables(self):
 
     def fix_version_3_tables(self):
         rdbms_common.Database.fix_version_3_tables(self)
-        self.sql('''CREATE INDEX words_both_idx ON public.__words
+        self.sql('''CREATE INDEX words_both_idx ON __words
             USING btree (_word, _textid)''')
 
     def _add_fts_table(self):