tools: Allow deleting of interfaces

tools: Allow deleting of interfaces

The frr-reload script currently deletes configurations
line-by-line under an interface context, if the interface was removed.
This approach fails when the interface has already been removed from the system.

This change enables whole interface removal using a single command
(no interface <interface-name>), simplifying the reload process and
reducing reload errors.

Signed-off-by: Julian Klaiber <jklaiber@open-systems.com>