README: remove description about CONFIG_USE_ARCH_MEMCPY/SET

These options are now described in the Kconfig help.  We do not want
to maintain duplicated documentation.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

README

@@ -4593,12 +4593,6 @@ Low Level (hardware related) configuration options:
 		addressable memory. This option causes some memory accesses
 		to be mapped through map_sysmem() / unmap_sysmem().
 
-- CONFIG_USE_ARCH_MEMCPY
-  CONFIG_USE_ARCH_MEMSET
-		If these options are used a optimized version of memcpy/memset will
-		be used if available. These functions may be faster under some
-		conditions but may increase the binary size.
-
 - CONFIG_X86_RESET_VECTOR
 		If defined, the x86 reset vector code is included. This is not
 		needed when U-Boot is running from Coreboot.