pgroonga: Remove now-unnecessary 'GRANT USAGE' statement.

This was only necessary for PGroonga 1.x, and the `pgroonga` schema
will most likely be removed at some point inthe future, which will
make this statement error out.

Drop the unnecessary statement.

(cherry picked from commit dc2726c814)

tools/setup/postgresql-init-dev-db

@@ -116,8 +116,6 @@ SELECT unnest(
         ARRAY['ALTER SYSTEM SET pgroonga.enable_wal = ''on''', 'SELECT pg_reload_conf()']
     END
 ) \gexec
-
-GRANT USAGE ON SCHEMA pgroonga TO $USERNAME;
 EOF
 
 psql -v ON_ERROR_STOP=1 -e -h localhost postgres "$USERNAME" <<EOF