RISC-V: defconfigs: Remove redundant CONFIG_EFI=y

We've always had CONFIG_EFI as "def_bool y" so this has always been
redundant.  It's removed by savedefconfig, so drop it to keep things
clean.

Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>