Remove pluggable-transports-linux{32,64}-debug.zip files
The pluggable-transports-linux{32,64}-debug.zip files built by gitian-pluggable-transports.yml, have, as far as I can tell, been empty zip files since I created the descriptors in #9444 (closed). They was there because I used gitian-tor.yml as a starting point; at the time I didn't know what tor-linux{32,64}-debug.zip were for, and I didn't know whether to take them out or leave them in. I think the files can be removed.