Update API to use (char *) for email addresses and hostnames

Update API to use (char *) for email addresses and hostnames

Reduces number of silly casts in OpenSSL code and likely most
applications.  Consistent with (char *) for "peername" value from
X509_check_host() and X509_VERIFY_PARAM_get0_peername().

(cherry picked from commit 297c67fcd817ea643de2fdeff4e434b050d571e2)