crypto: echainiv - Remove unused alg/spawn variable

This patch remove two unused variable and some dead "code" using it.

Fixes: 66008d42 ("crypto: echainiv - Remove AEAD compatibility code")
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>