[PluginManager] Small cleanup in callback prototypes
[PluginManager] Small cleanup in callback prototypes

gregier/libpeas,GNOME/libpeas,Distrotech/libpeas,chergert/libpeas,gregier/libpeas,Distrotech/libpeas,chergert/libpeas,GNOME/libpeas,chergert/libpeas,Distrotech/libpeas,gregier/libpeas,gregier/libpeas