Revert "EVP_*Update: ensure that input NULL with length 0 isn't passed"

This reverts commit dcb982d7

.

This change is causing extended tests to fail.

[extended tests]

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8964)

(cherry picked from commit 2c236894)