daklib/dbconn.py: Don't list install_date twice in not-null constraint.

diff --git a/daklib/dbconn.py b/daklib/dbconn.py
index 256ed4a9bd5c1b411be76364d0248c5ae278980b..a31e9167c6cd4671a55274be67188bc39ff0c521 100755 (executable)
--- a/daklib/dbconn.py
+++ b/daklib/dbconn.py
@@ -2480,7 +2480,7 @@ class DBSource(ORMObject):
 
     def not_null_constraints(self):
         return ['source', 'version', 'install_date', 'maintainer', \
-            'changedby', 'poolfile', 'install_date']
+            'changedby', 'poolfile']
 
     def read_control_fields(self):
         '''