usb: phy: samsung: remove old USB 2.0 PHY driver

drivers/usb/phy/phy-samsung-usb2 driver got replaced by
drivers/phy/phy-samsung-usb2 one and is no longer used.

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Vivek Gautam <gautam.vivek@samsung.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>