smdk5250: Remove 'board_usb_vbus_init()' function

smdk5250: Remove 'board_usb_vbus_init()' function

Previously as a part of moving the VBUS gpio support to device tree
following patch removed this and added relevant support in driver:
4a271cb exynos: usb: Switch USB VBUS GPIOs to be device tree configured

Recent changes for common board file migration for exynos platform
added it again. So removing it now.

Signed-off-by: Vivek Gautam <[email protected]>
Cc: Julius Werner <[email protected]>
Cc: Minkyu Kang <[email protected]>
Cc: Marek Vasut <[email protected]>
Signed-off-by: Minkyu Kang <[email protected]>