dt-bindings: phy: bcm-ns-usb2-phy: drop deprecated variant

dt-bindings: phy: bcm-ns-usb2-phy: drop deprecated variant

The old binding variant (the one covering whole DMU block) was
deprecated 3 years ago. Linux kernel was warning when using it for
similar amount of time.

There aren't any known Northstar devices with bootloader providing DT to
operating system. Actually OpenWrt seems to be the only project using
this binding and it always appends DTB to kernel. It has switched to the
non-deprecated binding years ago.

Given there is close to zero chance this breaks anyone's setup it should
more than safe to drop this binding variant after 3 years.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240913044557.28315-1-zajec5@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>