mod_sasl2_bind2, mod_sasl2_sm: Remove bind2 <features/> wrapper element
This was dropped from the spec. It's more consistent with SASL2.
This module blocks configured queries that change server state.
E.g. to make vCard storage read-only:
``` lua
readonly_stores = {
vcard = { "vcard-temp", "vCard" };
}
```