ARM: pxa: remove unused empty mach/pxa25x-udc.h file

Commit c5418a0b ("usb: gadget: pxa25x_udc: move register definitions
from arch") removed inclusion of mach/pxa25x-udc.h from the PXA25x UDC
driver, the contents of the header file was also wiped out, however the
file itself hasn't been removed, now this change removes the unused empty
header file.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>