lib: remove nb/yang memory cleanup when daemonizing

lib: remove nb/yang memory cleanup when daemonizing

We're not calling any other termination functions to free allocated
memory when daemonizing except these two. There's no reason for such an
exception, and because of these calls we have the following libyang
warnings every time FRR is started:
```
MGMTD: libyang: String "15" not freed from the dictionary, refcount 2
MGMTD: libyang: String "200" not freed from the dictionary, refcount 2
MGMTD: libyang: String "mrib-then-urib" not freed from the dictionary, refcount 2
MGMTD: libyang: String "1000" not freed from the dictionary, refcount 2
MGMTD: libyang: String "10" not freed from the dictionary, refcount 2
MGMTD: libyang: String "5" not freed from the dictionary, refcount 2
```

Remove these calls to get rid of the unnecessary warnings.

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