Fix g_type_class_add_private deprecation warnings
I see a lot of warnings while building, e.g:
[362/417] Compiling C object 'src/miners/fs/8409082@@tracker-miner-fs@exe/tracker-storage.c.o'.
../src/miners/fs/tracker-storage.c: In function ‘tracker_storage_class_init’:
../src/miners/fs/tracker-storage.c:136:2: warning: ‘g_type_class_add_private’ is deprecated [-Wdeprecated-declarations]
g_type_class_add_private (object_class, sizeof (TrackerStoragePrivate));
^~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/glib-2.0/gobject/gobject.h:24,
from /usr/include/glib-2.0/gobject/gbinding.h:29,
from /usr/include/glib-2.0/glib-object.h:23,
from /usr/include/glib-2.0/gio/gioenums.h:28,
from /usr/include/glib-2.0/gio/giotypes.h:28,
from /usr/include/glib-2.0/gio/gio.h:26,
from ../src/miners/fs/tracker-storage.c:24:
/usr/include/glib-2.0/gobject/gtype.h:1303:10: note: declared here
void g_type_class_add_private (gpointer g_class,
^~~~~~~~~~~~~~~~~~~~~~~~