webmin: remove perl-module-sdbm from RDEPENDS

Remove 'perl-module-sdbm' from RDEPENDS as perl don't build out this module.
This also fixes the following warning.

  WARNING: QA Issue: webmin rdepends on perl-module-sdbm, but it isn't a build dependency? [build-deps]

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>