dt-bindings: usb: Drop duplicate nvidia,tegra20-ehci.txt

The nvidia,tegra20-ehci binding is already documented in
ci-hdrc-usb2.yaml, so drop the old text binding.

Signed-off-by: "Rob Herring (Arm)" <robh@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250807214351.4172243-1-robh@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>