Removes support for sha1 signed kernel modules, importing sha1 signed
x.509 certificates.

rsa-pkcs1pad keeps sha1 padding support, which seems to be used by
virtio driver.

sha1 remains available as there are many drivers and subsystems using
it. Note only hmac(sha1) with secret keys remains cryptographically
secure.

In the kernel there are filesystems, IMA, tpm/pcr that appear to be
using sha1. Maybe they can all start to be slowly upgraded to
something else i.e. blake3, ParallelHash, SHAKE256 as needed.
Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@canonical.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>