[Bug12617] Remove gros-wattmetre1 & gros-wattmetre3

Related to bug12617.

Remove gros-wattmetre1 & gros-wattmetre3 from infra.

Removing theses two wattmetre broke the rake valid:homogeneity task, because nodes on gros-pdu2 have a wattmetre, and nodes on gros-pdu(1|3) doesn't have a wattmetre. So I added an exception in lib/refrepo/valid/data/homogeneity.rb so that it doesn't raise an error.