tplinker: ignore chat accounts handled by other providers
tplinker: ignore chat accounts handled by other providers

We don't want chat accounts handled by other providers (like Facebook or
Google ones) to appear twice, once through the “telepathy” provider and
once through the service-specific one.

https://bugzilla.gnome.org/show_bug.cgi?id=696267

halfline/gnome-online-accounts,ritzk/gnome-online-accounts,felipeborges/gnome-online-accounts,ritzk/gnome-online-accounts,dnohales/gnome-online-accounts,halfline/gnome-online-accounts,dnohales/gnome-online-accounts,ritzk/gnome-online-accounts,felipeborges/gnome-online-accounts,Distrotech/gnome-online-accounts,halfline/gnome-online-accounts,dnohales/gnome-online-accounts,Distrotech/gnome-online-accounts,felipeborges/gnome-online-accounts,Distrotech/gnome-online-accounts