ARM: tegra: Remove eMMC vmmc property for roth/tn7

This property was wrong and broke eMMC since commit 52221610 ("mmc:
sdhci: Improve external VDD regulator support"). Align the eMMC
properties to those of other Tegra boards.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>