ARM: dts: stm32: lxa: drop unnecessary vusb_d/a-supply

ARM: dts: stm32: lxa: drop unnecessary vusb_d/a-supply

The LXA device trees are the only STM32MP1 device tree that specify
vusb_d/usb_a-supply and apparently not for good reason:

- vusb_d-supply (vdd_usb) is the same as the phy-supply for usbphyc_port1
- vusb_a-supply (reg18) is the same as vdda1v8-supply for usbphyc_port1

and usbphyc_port1 is linked to the usbotg_hs node via the phys property.

Specifying the regulators in the &usbotg_hs node is thus superfluous and
has been even found to be harmful in one instance:
Linux v6.10 was found to lock up every 50-125 or so reboots on the LXA
TAC when the DWC2 driver probe enables the regulators in bulk, unless
both properties were removed.

This issue was so far not reproducible on v6.17 (> 500 reboots), but as
these properties are unnecessary and different from other STM32MP1
boards, remove them anyway.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.kernel.org/r/20251007-lxa-usb-dt-v1-1-cacde8088bb9@pengutronix.de
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>