distro/tegrademo-mender.conf: remove unneeded settings

which date back to the original attempt at integrating
Mender into the distro.  meta-mender-tegra now includes
the neeeded runtime dependencies, and any adjustments to
flash/SDcard space reservation (it already reserves 1MiB)
should be made there.

Signed-off-by: Matt Madison <matt@madison.systems>