Fix unoidl sourceprovider old-style service duplicate member checks

Change-Id: Ifa19a427543e76053e9b249c479e1e13f3599bcc
-Werror,-Wunused-private-field

...fixed more thoroughly than 49c1964b427c9f2f169ba4d826d346adc7555ae0 "WaE:
private field 'm_bCompoundControlChild' is not used."

Change-Id: Ief1093c054fe272b82da78ab103e8ca3feb72b90