l3cfg: remove tna_dirty member

The member is no longer used.

Fixes: 1feaf427d2 ('platform: rework handling of failed routes during nm_platform_ip_route_sync()')
(cherry picked from commit aed21d50af)

src/core/nm-l3cfg.c

@@ -168,7 +168,6 @@ typedef struct {
     /* This flag is only used temporarily to do a bulk update and
      * clear all the ones that are no longer in used. */
     bool os_dirty : 1;
-    bool os_tna_dirty : 1;
 } ObjStateData;
 
 G_STATIC_ASSERT(G_STRUCT_OFFSET(ObjStateData, obj) == 0);