trivial: remove RawSQL import, now unused

chrono/agendas/models.py

@@ -17,7 +17,6 @@
 from django.core.urlresolvers import reverse
 from django.db import models
 from django.db import transaction
-from django.db.models.expressions import RawSQL
 from django.utils.formats import date_format
 from django.utils.text import slugify
 from django.utils.timezone import localtime, now