conductor: remove `GossipNetwork` from `Driver`

[noot]

see discussion here: #106 (comment)

these may also be relevant:

• addition of Exclusive to sync: [core] add Exclusive to sync rust-lang/rust#97629
• rust internals discussion: https://internals.rust-lang.org/t/what-shall-sync-mean-across-an-await/12020

[joroshiba]

With #325 deciding not to implement gossipnet, this is no longer necessary. The new work to connect to sequencer should likely be done outside of Driver.