Hello Guix,

Starting on version 0.4.3.5, Tor provides a configuration flag to
disable relay code (--disable-module-relay). Considering most
people are running clients, not relays, I thought it would be
nice for guix to have a client-only package definition (maybe
it could even be the default?). What do you think?

I've tested the code below and it works as expected on my guix
install. However, since I'm neither a schemer nor guixpert, fell
free to teach me how to do it the guix way.

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