remove haveged from SITE_PACKAGES

As per Gluon recommendation, remove haveged from SITE_PACKAGES:
> Starting with version 19.07 OpenWrt ships the urngd entropy daemon by
> default. It replaces the haveged daemon, for which we removed the
> support in Gluon. Remove haveged from your package selection.

Reference: https://gluon.readthedocs.io/en/latest/releases/v2020.2.html#site-mk