core: Remove GetEventNotificationMethods

GetEventNotificationMethodsQuery is not used anywhere in
the code, and hence should be removed.

This patch removes the following:
1. The GetEventNotificationMethodsQuery class.
2. The GetEventNotificationMethods constant representing
   it in VdcQueryType.
3. The getAllEventNotificationMethods() method in EvetDAO, its
   implementation, test and underlying stored procedure, as this
   method was only used by the aforementioned query.

Signed-off-by: Allon Mureinik <amureini@redhat.com>
Change-Id: I9ab37e8fb5a1602b0d8d0d9b1107c596dd33093b