zebra: drop the SVI MAC cleanup done as a part of interface delete

zebra: drop the SVI MAC cleanup done as a part of interface delete

As a part of FRR shutdown interfaces are force flushed (in an arbitary
order). Interfaces are already down at that point i.e. resources like
SVI-MAC have already been released. Attempting to clean it up again
as a part of the force-flush was resulting in access of freed up memory -

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
==26457== Thread 1:
==26457== Invalid read of size 8
==26457==    at 0x1AE6B0: zebra_evpn_acc_bd_svi_set (zebra_evpn_mh.c:606)
==26457==    by 0x1B1460: zebra_evpn_if_cleanup (zebra_evpn_mh.c:1040)
==26457==    by 0x13CA69: if_zebra_delete_hook (interface.c:244)
==26457==    by 0x48A0E34: hook_call_if_del (if.c:59)
==26457==    by 0x48A0E34: if_delete_retain (if.c:290)
==26457==    by 0x48A2F94: if_delete (if.c:313)
==26457==    by 0x48A3169: if_terminate (if.c:1217)
==26457==    by 0x48E0024: vrf_delete (vrf.c:254)
==26457==    by 0x48E0024: vrf_delete (vrf.c:225)
==26457==    by 0x48E02FE: vrf_terminate (vrf.c:551)
==26457==    by 0x1442E1: sigint (main.c:203)
==26457==    by 0x1442E1: sigint (main.c:141)
==26457==    by 0x48CF862: quagga_sigevent_process (sigevent.c:103)
==26457==    by 0x48DD324: thread_fetch (thread.c:1404)
==26457==    by 0x48A926A: frr_run (libfrr.c:1122)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
(gdb) bt
(gdb) fr 5
1037    zebra/zebra_evpn_mh.c: No such file or directory.
(gdb) p zif->ifp->name
$2 = "vlan131", '\000' <repeats 12 times>
(gdb) p zif->link->info
$5 = (void *) 0x1
(gdb) p/x zif->ifp->flags
$7 = 0x1002
(gdb)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Ticket: CM-32435

Signed-off-by: Anuradha Karuppiah <anuradhak@nvidia.com>