This revised query should give you what you need:
SELECT 'ALTER TABLE ' || quote_ident(n.nspname) || '.'
|| quote_ident(c.relname)
|| ' ALTER COLUMN ' || quote_ident(a.attname) || ' TYPE varchar(' || i.character_maximum_length || ');'
FROM pg_class c
JOIN pg_namespace n ON n.oid = c.relnamespace
JOIN pg_attribute a ON a.attrelid = c.oid
JOIN pg_type t ON t.oid = a.atttypid
JOIN information_schema.columns i ON (i.table_name = c.relname AND i.column_name = a.attname)
WHERE t.typname = 'bpchar'
AND c.relkind = 'r'
AND n.nspname <> 'pg_catalog' and not attisdropped;