remove redundant import that current rust nightly complains about

[aurelj]

Current rust nightly complains about some redundant imports, so just remove these imports.
I've checked that these imports are not needed, even on rust stable.

$ rustc --version
rustc 1.79.0-nightly (ab5bda1aa 2024-04-08)
$ cargo check
    Checking tmq v0.4.0 (/home/aurel/devel/embedded/tmq)
warning: the item `zmq` is imported redundantly
 --> src/socket_types/dealer.rs:1:11
  |
1 | use zmq::{self, Context as ZmqContext};
  |           ^^^^ the item `zmq` is already defined by prelude
  |
  = note: `#[warn(unused_imports)]` on by default

warning: the item `zmq` is imported redundantly
 --> src/socket_types/pair.rs:1:11
  |
1 | use zmq::{self, Context as ZmqContext};
  |           ^^^^ the item `zmq` is already defined by prelude

warning: the item `zmq` is imported redundantly
 --> src/socket_types/publish.rs:1:11
  |
1 | use zmq::{self, Context as ZmqContext};
  |           ^^^^ the item `zmq` is already defined by prelude

warning: the item `zmq` is imported redundantly
 --> src/socket_types/pull.rs:1:11
  |
1 | use zmq::{self, Context as ZmqContext};
  |           ^^^^ the item `zmq` is already defined by prelude

warning: the item `zmq` is imported redundantly
 --> src/socket_types/push.rs:1:11
  |
1 | use zmq::{self, Context as ZmqContext};
  |           ^^^^ the item `zmq` is already defined by prelude

warning: the item `zmq` is imported redundantly
 --> src/socket_types/request_reply.rs:4:11
  |
4 | use zmq::{self, Context as ZmqContext};
  |           ^^^^ the item `zmq` is already defined by prelude

warning: the item `zmq` is imported redundantly
 --> src/socket_types/router.rs:1:11
  |
1 | use zmq::{self, Context as ZmqContext};
  |           ^^^^ the item `zmq` is already defined by prelude

warning: the item `zmq` is imported redundantly
 --> src/socket_types/subscribe.rs:1:11
  |
1 | use zmq::{self, Context as ZmqContext};
  |           ^^^^ the item `zmq` is already defined by prelude

warning: `tmq` (lib) generated 8 warnings
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 13.18s