Drop support for CONFIG_SKIP_RELOCATE_UBOOT

For ARM systems, before ELF relocation was introduced,
CONFIG_SKIP_RELOCATE_UBOOT coul be used to prevent *COPYING* the
U-Boot image from whereever it was loaded to it's link address
(CONFIG_SYS_TEXT_BASE).  The name was badly chosen, as no relocation
was performed at all, it was just a memcpy().

With ELF relocation, this does not work like that any more, and
related boards need to be fixed anyway.  So don't keep this relict any
longer.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Tested-by: Heiko Schocher <hs@denx.de>
Tested-by: Reinhard Meyer <u-boot@emk-elektronik.de>