Remove unneeded SPAKE free_modreq method

Commit ff57dc682a27bd205d715f3c0bed84890f2453c4 removed the use of
per-request module data in SPAKE, but neglected to remove the
corresponding free_modreq method.

https://github.com/krb5/krb5/commit/1465dbd8fc88cf31af3579f09a3148da3b9e1c3e
Author: Greg Hudson <ghudson@mit.edu>
Commit: 1465dbd8fc88cf31af3579f09a3148da3b9e1c3e
Branch: master
 src/plugins/preauth/spake/spake_kdc.c |    9 ---------
 1 files changed, 0 insertions(+), 9 deletions(-)