crypto: streebog - remove two unused variables

crypto/streebog_generic.c:162:17: warning:
 Pi defined but not used [-Wunused-const-variable=]
crypto/streebog_generic.c:151:17: warning:
 Tau defined but not used [-Wunused-const-variable=]

They are never used, so can be removed.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Vitaly Chikunov <vt@altlinux.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>