Fix deprecated warnings

Fix all but two deprecation warnings. These two can't be fixed mechanically, and need an intervention:

../eek/eek-keyboard.c:393:5: warning: ‘g_type_class_add_private’ is deprecated [-Wdeprecated-declarations] ../eekboard/eekboard-context-service.c:359:5: warning: ‘g_type_class_add_private’ is deprecated [-Wdeprecated-declarations]