libsysprof-capture: Use sysprof_{steal,clear}_pointer() instead of GLib

They work exactly the same way as the GLib functions.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #40

src/libsysprof-capture/sysprof-capture-condition.c

@@ -221,7 +221,7 @@ sysprof_capture_condition_init (void)
 
   self->ref_count = 1;
 
-  return g_steal_pointer (&self);
+  return sysprof_steal_pointer (&self);
 }
 
 /* Returns NULL on allocation failure. */