Revert "ripd: Cleanup memory allocations on shutdown"

Revert "ripd: Cleanup memory allocations on shutdown"

This reverts commit 3d1588d8ed537e3dbf120e1b2a5ad5b3c00c7897.

This commit introduced a crash. When the VRF is deleted, the RIP instance
should not be freed, because the NB infrastructure still stores the
pointer to it. The instance should be deleted only when it's actually
deleted from the configuration.

To reproduce the crash:
```
frr# conf t
frr(config)# vrf vrf1
frr(config-vrf)# exit
frr(config)# router rip vrf vrf1
frr(config-router)# exit
frr(config)# no vrf vrf1
frr(config)# no router rip vrf vrf1
vtysh: error reading from ripd: Resource temporarily unavailable (11)Warning: closing connection to ripd because of an I/O error!
frr(config)#
```

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>