varlink-cli: Drup unneeded Vec creation

Fixes clippy warning:

```rust
warning: useless use of `vec!`
   --> varlink-cli/src/watchclose_epoll.rs:157:21
    |
157 |         let mut v = vec![Event { events: 0, data: 0 }, Event { events: 0, data: 1 }];
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: you can use an array directly: `[Event { events: 0, data: 0 }, Event { events: 0, data: 1 }]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_vec
    = note: `#[warn(clippy::useless_vec)]` on by default
```

varlink-cli/src/watchclose_epoll.rs

@@ -154,7 +154,7 @@ impl WatchClose {
 
 impl Read for WatchClose {
     fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
-        let mut v = vec![Event { events: 0, data: 0 }, Event { events: 0, data: 1 }];
+        let mut v = [Event { events: 0, data: 0 }, Event { events: 0, data: 1 }];
 
         'outer: loop {
             let r = epoll_wait(self.efd, -1, &mut v[..])?;