Revert "module: sign with sha512 instead of sha1 by default"

This reverts commit 7c2f874c which is
commit f3b93547 upstream.

It breaks the Android kernel build as BoringSSL can only sign with SHA1
for this Android branch, and we do not want to break the ABI by changing
the module signing process in this stable kernel branch.

It was only added upstream by Greg to get his ARM64 stable builds to
compile properly on the latest version of Fedora, which did NOT like to
sign with SHA1, so blame him :)

Bug: 161946584
Change-Id: I4901a37dd9ac4bdd54a712331e1288053f0d9fb9
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>