config: Remove Bridge <-> ClientTransportPlugin validation

This validation was only done if DisableNetwork was off because we would use
the global list of transports/bridges and DisableNetwork would not populate
it.

This was a problem for any user using DisableNetwork which includes Tor
Browser and thus leading to the Bug() warning.

Without a more in depth refactoring, we can't do this validation without the
global list.

The previous commit makes it that any connection to a bridge without a
transport won't happen thus we keep the security feature of not connecting to
a bridge without its corresponding transport.

Related to #40106

Signed-off-by: David Goulet <dgoulet@torproject.org>