ARM: tegra: remove UART5/UARTE from tegra124.dtsi

Tegra124 only has 4 UARTs. Parts of the documentation hint at a fifth
UART, but this appears to be left-over from earlier SoC documentation.
Remove the non-existent DT node for UART5.

Cc: <stable@vger.kernel.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>