core: Removed MigrateIrsSnapshotsToVdcCommand

This command is unused (and all its content is commented out anyway),
and thus can (and should be removed).

This patch removes the following:
1. The MigrateIrsSnapshotsRoVdcCommand class
2. The corresponding constant in VdcActionType

Change-Id: I6584a79c777c8b44c23159850d133c7c514b5c87
Signed-off-by: Allon Mureinik <amureini@redhat.com>