powerpc/configs/skiroot: Drop default n CONFIG_CRYPTO_ECHAINIV

It's default n so we don't need to disable it.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20200121043000.16212-5-mpe@ellerman.id.au