Remove use strict and use warnings from the Shibboleth.pm module.

Don't worry.  The module is still strict and has warnings enabled.  All
modules that derive from `Mojo::Base` are.  I forgot to remove these
when changing to that, and those cause warnings since Mojo::Base
disables the warnings for using signatures.

lib/WeBWorK/Authen/Shibboleth.pm

@@ -32,9 +32,6 @@ C<conf/authen_shibboleth.conf.dist> file.
 
 =cut
 
-use strict;
-use warnings;
-
 use Digest;
 
 use WeBWorK::Debug qw(debug);