configs: k3: Remove saved environments

Having saved environments usually causes inconsistencies while in
development workflow. The saved environments conflict with the
default ones that U-boot should be updating during development
but that doesn't happen and the saved environments need to be
reset during bootups to test the changes causing extra debugs.

Remove the saved environments as a default. Environments can always
be re-enabled locally if one does like them or needs them for
some production environment. Optionally, Uenv.txt can also be used on
some of the boot media.

Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>