parser: Drop a pointless macro
parser: Drop a pointless macro

The JSON_PARSER_GET_PRIVATE macro is pointless, now that we use the new
version of GLib.

Distrotech/json-glib,frida/json-glib,GNOME/json-glib,Distrotech/json-glib,ebassi/json-glib,Distrotech/json-glib,ebassi/json-glib,frida/json-glib,ebassi/json-glib,GNOME/json-glib