Remove support for CONFIG_HAS_UID and "forceenv" command

This (undocumented) concept was only in use for the MVSMR and
davinci_schmoogie Sergey Kubushyn <ksi@koi8.net> boards.
Drop it for now.  If really needed, it should be reimplemented
later in the context of the new environment command set.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Andre Schwarz <andre.schwarz@matrix-vision.de>
Cc: Sergey Kubushyn <ksi@koi8.net>
Acked-by: Sergey Kubushyn <ksi@koi8.net>