Remove KRB5-dependency for now

We still depend on it, but our unit tests are failing on other module repositories and it makes no sense to install it on all of them

Author: tvdijen

composer.json

@@ -28,7 +28,6 @@
     },
     "require": {
         "php": ">=5.6",
-        "ext-krb5": "*",
 
         "simplesamlphp/composer-module-installer": "~1.1",
         "simplesamlphp/simplesamlphp-module-ldap": "^0.9",