ARM: dts: remove old USB2 PHY node for exynos5250

drivers/usb/phy/phy-samsung-usb2 driver got replaced by
drivers/phy/phy-samsung-usb2 one.  Remove the leftover
USB2 PHY node (EHCI/OHCI USB nodes are using the new one
already) from Exynos5250 dtsi file.

Cc: Mark Brown <broonie@linaro.org>
Cc: Kamil Debski <k.debski@samsung.com>
Cc: Vivek Gautam <gautam.vivek@samsung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Vivek Gautam <gautam.vivek@samsung.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>